#include <bits/stdc++.h>
#define NMAX 100010
using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
vector<int> G[NMAX],comp[NMAX];
int n,m;
int nrcomp,nr;
bitset <NMAX> viz;
int ord[NMAX], low[NMAX],pas=0;
stack <int> stk;
void Tarjan(int x){
    ord[x] = low [x] = ++pas;
    viz[x]=true;
    stk.push(x);
    for(auto it: G[x]){
        if(ord[it])
            if(viz[it])
                low[x]=min(low[x],low[it]);
            else;
        else{
            Tarjan(it);
            low[x]=min(low[x],low[it]);
        }
    }
    if(low[x]==ord[x]){
        nrcomp++;
        int stktop;
        do{
            stktop=stk.top();
            stk.pop();
            viz[stktop]=false;
            comp[nrcomp].push_back(stktop);
        }while(stktop != x);
    }
}
void citire(){
    f>>n>>m;
    for(int i=1,x,y;i<=m;i++){
        f>>x>>y;
        G[x].push_back(y);
    }
}
void afisare(){
    g<<nrcomp<<"\n";
    for(int i=1;i<=nrcomp;i++){
        for(int j=0;j<comp[i].size();j++){
            g<<comp[i][j]<<" ";
        }
        g<<"\n";
    }
}
int main()
{
    citire();
    for(int i=1;i<=n;i++)
        if(!ord[i])Tarjan(i);
    afisare();
    return 0;
}