#include <bits/stdc++.h>
using namespace std;
ifstream r("ctc.in");
ofstream w("ctc.out");
int d[100001],n, o, nr, m;
bool v[100001];
vector<int>a[100001],a2[100001],c[100001];
void f(int x)
{
    if(v[x]==0)
    {
        v[x]=1;
        for(auto it:a[x]){
            f(it);
        }
        nr++;
        d[nr]=x;
    }
}
void g(int x)
{
    if(v[x]==0)
    {
        v[x]=0;
        for(auto it: a2[x]){
            g(it);
        }
        c[o].push_back(x);
    }
}
int main()
{
    r>>n>>m;
    int x,y,i;
    while(r>>x>>y){
        a[x].push_back(y);
        a2[y].push_back(x);
    }
    for(i=1; i<=n; i++){
        f(i);
    }
    for(i=n; i>=1; i--){
        if(v[d[i]])
        {
            o++;
            g(d[i]);
        }
    }
    w<<o<<"\n";
    for(i=1; i<=o; i++)
    {
        for(auto it: c[i]){
            w<<it<<" ";
        }
        w<<"\n";
    }
    return 0;
}