C :

#include <stdio.h>
int a[510][510];
int main()
{
	int n,m,i,j,u,v,n1,k;
	while (scanf("%d %d",&n,&m)&&n)
	{
		for (i=0;i<=n;i++)
			for (j=1;j<=n;j++)
			{
				if (i==0) a[i][j]=1;
				else a[i][j]=0;
			}
		for (i=0;i<m;i++)
		{
			scanf("%d %d",&u,&v);
			a[u][v]++;
		}
		n1=n;
		while (n1--)
		{
			for (i=1;i<=n;i++)
			{
				if (a[0][i]==1)
				{
					for (j=1;j<=n;j++)
						if (a[j][i]!=0) break;
				}
				if ((j==n+1)&&(a[0][i]==1)) 
				{
					a[0][i]=0;
					for (k=1;k<=n;k++)
					{
						if (a[i][k]!=0)
							a[i][k]--;
					}
					if (n1>0) printf("%d ",i);
					else printf ("%d\n",i);
					break;
				}
			}
		}
	}
	return 0;
}

C++ :

#include <stdio.h>
#include <vector>
#include <queue>
using namespace std;

int indegree[505];
vector<int> edge[505];
priority_queue<int , vector<int> , greater<int> > Q;

int main()
{
	int output[505];
	int n,m,i;
	while(scanf("%d%d",&n,&m)!=-1)
	{
		if(n==0 && m==0)
			break;
		
		for(i=1;i<=n;i++)
		{
			indegree[i]=0;
			edge[i].clear();
			output[i]=0;
		}
		
		while(m--)
		{
			int a,b;
			scanf("%d%d",&a,&b);
			edge[a].push_back(b);
			indegree[b]++;
		}
		
		while(!Q.empty())
			Q.pop();
		
		for(i=1;i<=n;i++)
		{
			if(indegree[i]==0)
				Q.push(i);
		}
		
		int size=0;
		while(!Q.empty())
		{
			int tmp=Q.top();
			Q.pop();
			output[size++]=tmp;
			for(i=0;i<edge[tmp].size();i++)
			{
				indegree[edge[tmp][i]]--;
				if(indegree[edge[tmp][i]]==0)
					Q.push(edge[tmp][i]);
			}
		}
		
		for(i=0;i<size;i++)
		{
			if(i)
				printf(" %d",output[i]);
			else
				printf("%d",output[i]);
		}
		
		printf("\n");
	}
	return 0;
}