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package class16;
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// 课上没讲这个实现
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// 因为是一样的，都是根据入度来求拓扑排序，只不过是牛客网的测试数据
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// 测试链接 : https://www.nowcoder.com/questionTerminal/88f7e156ca7d43a1a535f619cd3f495c
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// 请同学们务必参考如下代码中关于输入、输出的处理
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// 这是输入输出处理效率很高的写法
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// 提交以下所有代码，把主类名改成Main，可以直接通过
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import java.io.BufferedReader;
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import java.io.IOException;
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import java.io.InputStreamReader;
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import java.io.OutputStreamWriter;
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import java.io.PrintWriter;
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import java.io.StreamTokenizer;
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import java.util.ArrayList;
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import java.util.Arrays;
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public class Code03_TopologicalOrderBFS2 {
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public static int MAXN = 200001;
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public static int[] queue = new int[MAXN];
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public static int[] indegree = new int[MAXN];
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public static int[] ans = new int[MAXN];
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public static int n, m, from, to;
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public static void main(String[] args) throws IOException {
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BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
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StreamTokenizer in = new StreamTokenizer(br);
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PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
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while (in.nextToken() != StreamTokenizer.TT_EOF) {
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n = (int) in.nval;
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in.nextToken();
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m = (int) in.nval;
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ArrayList<ArrayList<Integer>> graph = new ArrayList<>();
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for (int i = 0; i <= n; i++) {
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graph.add(new ArrayList<>());
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}
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for (int i = 0; i < m; i++) {
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in.nextToken();
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from = (int) in.nval;
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in.nextToken();
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to = (int) in.nval;
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graph.get(from).add(to);
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}
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if (!topoSort(graph)) {
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out.println(-1);
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} else {
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for (int i = 0; i < n - 1; i++) {
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out.print(ans[i] + " ");
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}
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out.println(ans[n - 1]);
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}
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out.flush();
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}
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}
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// 有拓扑排序返回true
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// 没有拓扑排序返回false
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public static boolean topoSort(ArrayList<ArrayList<Integer>> graph) {
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Arrays.fill(indegree, 1, n + 1, 0);
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for (ArrayList<Integer> nexts : graph) {
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for (int next : nexts) {
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indegree[next]++;
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}
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}
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int l = 0;
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int r = 0;
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for (int i = 1; i <= n; i++) {
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if (indegree[i] == 0) {
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queue[r++] = i;
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}
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}
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int cnt = 0;
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while (l < r) {
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int cur = queue[l++];
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ans[cnt++] = cur;
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for (int next : graph.get(cur)) {
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if (--indegree[next] == 0) {
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queue[r++] = next;
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}
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}
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}
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return cnt == n;
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}
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}
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