#include<cstdio>
#include<cstring>
using namespace std;
struct node
{
    int x,y,next;
}a[1300000];int len,first[5100];
int cnt,belong[21000];
int id,dfn[21000],low[21000],b[5100];
int tp,sta[21000]; bool v[21000];
int ru[21000],chu[21000];
void ins(int x,int y)
{
	len++;
	a[len].x=x; a[len].y=y;
	a[len].next=first[x];
	first[x]=len;
}
int mymin(int x,int y)
{
	return x>y?y:x;
}
void dfs(int x)
{
	low[x]=dfn[x]=++id;
	sta[++tp]=x; v[x]=true;
	for(int k=first[x];k ;k=a[k].next)
	{
		int y=a[k].y;
		if(dfn[y]==-1)
		{
			dfs(y);
			low[x]=mymin(low[x],low[y]);
		}
		else if(v[y])
		{
			low[x]=mymin(low[x],dfn[y]);
		}
	}
	if(low[x]==dfn[x])
	{
		cnt++;
		int i;
		do{
			i=sta[tp--];
			v[i]=false;
			belong[i]=cnt;
		}while(i!=x);
	}
}
int main()
{
	int cc,n,m,x,y,i;
	while(scanf("%d",&n)!=EOF)
	{
		if(n==0) break;
		scanf("%d",&m);
		len=0; memset(first,0,sizeof(first));
		for(i=1;i<=m;i++)
        {
            scanf("%d%d",&x,&y);
            ins(x,y);
        }
        id=tp=cnt=0;
        memset(low,0,sizeof(low));
        memset(dfn,-1,sizeof(dfn));
        memset(belong,0,sizeof(belong));
        memset(v,false,sizeof(v));
        for(i=1;i<=n;i++)
           if(dfn[i]==-1)
               dfs(i);
        memset(ru,0,sizeof(ru));
        memset(chu,0,sizeof(chu));
        for(i=1;i<=len;i++)
           if(belong[ a[i].x ] != belong[ a[i].y ] )
           {
              chu[belong[a[i].x]]++;
              ru[belong[a[i].y]]++;
           }
        int blen=0;
        for(i=1;i<=n;i++)
        {
        	if(chu[belong[i]]==0)
        	{
        		b[++blen]=i;
        	}
        }
        if(blen==0) printf("\n");
        else
        {
        	for(i=1;i<blen;i++) printf("%d ",b[i]);
        	printf("%d\n",b[blen]);
		}
    }
    return 0;
}