#include <bits/stdc++.h>
using namespace std;

ifstream fin("ctc.in");
ofstream fout("ctc.out");

const int dim=1e5+9;

vector<int>v[dim];
stack<int>stiva;

int nr_comp;
vector<int>comp[dim];

bool vizitat[dim],ap_stiva[dim];
int timp,low[dim],disc[dim];

void dfs(int x){
    vizitat[x]=true;
    disc[x]=low[x]=++timp;

    stiva.push(x);
    ap_stiva[x]=true;

    for(int y:v[x]){
        if(!vizitat[y]){
            dfs(y);
            low[x]=min(low[x],low[y]);
        }
        else{
            if(ap_stiva[y]){
                low[x]=min(low[x],disc[y]);
            }
        }
    }

    if(low[x]==disc[x]){
        nr_comp++;
        while(stiva.top()!=x){
            comp[nr_comp].push_back(stiva.top());
            ap_stiva[stiva.top()]=false;
            stiva.pop();
        }
        comp[nr_comp].push_back(stiva.top());
        ap_stiva[stiva.top()]=false;
        stiva.pop();
    }
}

signed main(){
    int n,m;
        fin>>n>>m;
    for(int i=1;i<=m;i++){
        int x,y;
        fin>>x>>y;
        v[x].push_back(y);
    }
    for(int i=1;i<=n;i++){
        if(!vizitat[i]){
            dfs(i);
        }
    }
        fout<<nr_comp<<'\n';
    for(int i=1;i<=nr_comp;i++){
        for(int x:comp[i]){
            fout<<x<<' ';
        }
        fout<<'\n';
    }
}