#include<stdio.h>

#include<string.h>

#include<vector>

#include<stack>

#include<set>

using namespace std;

#define MAX_NODE 5005

#define min(a, b) a < b? a:b

#define max(a, b) a > b? a:b

vector<int> gGraph[MAX_NODE];

stack<int> gStack;

int gDfn[MAX_NODE];

int gLow[MAX_NODE];

bool gVisited[MAX_NODE];

bool gInStack[MAX_NODE];

int gClusterOfNode[MAX_NODE];

int gIndex;

int gClusterIndex;

//Tarjan算法求强连通分支

void Tarjan(int u){

	gDfn[u] = gLow[u] = ++gIndex;

	gInStack[u] = true;

	gVisited[u] = true;

	gStack.push(u);

	for (int i = 0; i < gGraph[u].size(); i++){

		int v = gGraph[u][i];

		if (!gVisited[v]){

			Tarjan(v);

			gLow[u] = min(gLow[u], gLow[v]);

		}

		else if (gInStack[v]){

			gLow[u] = min(gLow[u], gDfn[v]);

		}

	}

	if (gDfn[u] == gLow[u]){

		int v;

		do{

			v = gStack.top();

			gStack.pop();

			gInStack[v] = false;

			gClusterOfNode[v] = gClusterIndex;

		} while (v != u);

		++gClusterIndex;

	}

}

vector<set<int> >gLinkFrom;	//每个强连通分支，入点集合

vector<set<int> > gLinkTo;	//每个强连通分支，出点集合

void ReconstructGraph(int nodes, int clusters){

	gLinkFrom.clear();

	gLinkFrom.resize(clusters);

	gLinkTo.clear();

	gLinkTo.resize(clusters);

	for (int u = 1; u <= nodes; u++){

		for (int i = 0; i < gGraph[u].size(); i++){

			int v = gGraph[u][i];

			int uc = gClusterOfNode[u];

			int vc = gClusterOfNode[v];

			if (uc != vc){	//注意！！！

				gLinkTo[uc].insert(vc);

				gLinkFrom[vc].insert(uc);

			}

		}

	}

}

int main(){

	int n, r;

	while (scanf("%d", &n) && n != 0){

		scanf("%d", &r);

		for (int i = 0; i <= n; i++){

			gGraph[i].clear();

		}

		int u, v;

		for (int i = 0; i < r; i++){

			scanf("%d %d", &u, &v);

			gGraph[u].push_back(v);

		}

		memset(gVisited, false, sizeof(gVisited));

		memset(gInStack, false, sizeof(gInStack));

		gIndex = gClusterIndex = 0;

		for (int i = 1; i <= n; i++){

			if (!gVisited[i])

				Tarjan(i);

		}

		ReconstructGraph(n, gClusterIndex);	//将染色后的图进行重构（即设置强连通分支）

		set<int> zero_outdegree_cluster_id;	//出度为0的强连通分支的集合

		for (int i = 0; i < gClusterIndex; i++){

			if (gLinkTo[i].empty()){	//出度为0，强连通分支

				zero_outdegree_cluster_id.insert(i);

			}

		}

		//遍历每个点，判断其是否属于那些出度为0的强连通分支

		for (int u = 1; u <= n; u++){

			if (zero_outdegree_cluster_id.find(gClusterOfNode[u]) != zero_outdegree_cluster_id.end()){

				printf("%d ", u);

			}

		}

		printf("\n");

	}

	return 0;

}