#include<cstdio>
#include<vector>

int n,m,i,x,y,ord[100001],nc;
::std::vector<int> a[100001],ta[100001];
::std::vector<int> c[100001];

bool viz[100001];

void DF(int v)
{
	viz[v] = 1;
	for(int i = 0;i<a[v].size();++i)
		if(!viz[a[v][i]])
			DF(a[v][i]);
	ord[++m] = v;
}

void DFT(int v)
{
	viz[v] = 1;
	c[nc].push_back(v);
	for(int i = 0;i<ta[v].size();++i)
		if(!viz[ta[v][i]])
			DFT(ta[v][i]);
}

int main()
{
	freopen("ctc.in","r",stdin);
	freopen("ctc.out","w",stdout);
	scanf("%d %d",&n,&m);
	++m;
	while(--m)
	{
		scanf("%d %d",&x,&y);
		a[x].push_back(y);
		ta[y].push_back(x);
	}
	for(i=1;i<=n;++i)
		if(!viz[i])
			DF(i);
	memset(viz,0,sizeof(viz));
	for(i=n;i>0;--i)
		if(!viz[ord[i]])
		{
			++nc;
			DFT(ord[i]);
		}
	printf("%d\n",nc);
	for(i=1;i<=nc;++i)
	{
		for(int j=0;j<c[i].size();++j)
			printf("%d ",c[i][j]);
		printf("\n");
	}
	fclose(stdout);
	return 0;
}