bool Topo()
{
	int sum = 0;
	while(1)
	{
		queue <int> Q;
		for(int i = 1; i <= n; i++)
			if(!in[i])
				Q.push(i);
		sum += Q.size();
		if(sum == n)
			return true;
		if(!Q.size())
			return false;
		while(!Q.empty())
		{
			int u = Q.front(); Q.pop();
			in[u]--;
			for(int v = first[u]; v != -1; v = e[v].next)
			{
				in[e[v].v]--;
			}
		}
	}
}