#include<cstdio>
#include<vector>
using namespace std;
const int N=100001;
vector<int> s[N],u[N],v[N];
int n,m,a[N],c,r,x,y,i,j;
bool b[N];
void A(int i)
{
    if(b[i])
		return;
	int j,k;
	for(b[i]=1,k=u[i].size(),j=0;j<k;j++)
		A(u[i][j]);
    a[++c]=i;
}
void B(int i)
{
    if(!b[i])
		return;
	int j,k;
	for(b[i]=j=0,k=v[i].size();j<k;j++)
    	B(v[i][j]);
    s[r].push_back(i);
}
int main()
{
    freopen("ctc.in","r",stdin),freopen("ctc.out","w",stdout),scanf("%d%d",&n,&m);
    while(m--)
    	scanf("%d%d",&x,&y),u[x].push_back(y),v[y].push_back(x);
    for(i=1;i<=n;i++)
		A(i);
    for(i=n;i;i--)
		if(b[a[i]])
			r++,B(a[i]);
	for(printf("%d\n",r),i=r;i;i--)
	{
		for(c=s[i].size(),j=0;j<c;j++)
			printf("%d ",s[i][j]);
		printf("\n");
	}
}