UVa 10305

#include<iostream>
#include<cstdio>
#include<vector>
#include<queue>

using namespace std;
const int maxn = 1005;
vector<int> ans;
int n, m, G[maxn][maxn], inDgree[maxn];

bool topsort()
{
	queue<int> q;
	int cnt = 0;
	
	for (int i = 1; i < n; i++)
	{
		if (inDgree[i] == 0)
			q.push(i);
	}

	while (!q.empty())
	{
		int u = q.front();
		q.pop();
		ans.push_back(u);
		cnt++;
		for (int i = 1; i <= n; i++)
		{
			if (G[u][i])
			{
				G[u][i] = 0;
				if (--inDgree[i] == 0)
					q.push(i);
			}
		}

	}
	if (cnt != n)
		return false;
	else
		return true;
}

int main()
{
	while (scanf("%d%d", &n, &m) && n)
	{
		memset(G, 0, sizeof(G));
		memset(inDgree, 0, sizeof(inDgree));

		int u, v;
		for (int i = 0; i < m; i++)
		{
			cin >> u >> v;
			G[u][v] = 1;
			inDgree[v]++;

		}

		ans.clear();
		if (topsort())
		{
			printf("%d", ans[0]);
			for (int i = 1; i < n; i++)
			{
				printf("%d", ans[i]);
			}
			cout << endl;
		}
		else
			printf("No\n");
	}

	return 0;
}