#include <bits/stdc++.h>
#define pb push_back

using namespace std;

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

const int nmax=1e5;

vector<int>v[nmax+1],c[nmax+1];

int timer,d[nmax+1],low[nmax+1],comp;
bool on_stack[nmax+1];
stack<int>st;

void get_scc(int nod){
    int t;
    comp++;
    do{
        t=st.top();
        st.pop();
        on_stack[t]=0;
        c[comp].pb(t);
    }while(t!=nod);
}

void tarjan(int nod){
    d[nod]=low[nod]=++timer;
    st.push(nod);
    on_stack[nod]=1;
    for(int i:v[nod]){
        if(d[i])
            low[nod]=min(low[nod],d[i]);
        else{
            tarjan(i);
            low[nod]=min(low[nod],low[i]);
        }
    }
    if(low[nod]==d[nod])
        get_scc(nod);
}


int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    int n,m;
    fin>>n>>m;
    while(m--){
        int st,dr;
        fin>>st>>dr;
        v[st].pb(dr);
    }
    for(int i=1;i<=n;i++)
        if(!d[i])
            tarjan(i);
    fout<<comp<<'\n';
    for(int i=1;i<=comp;i++){
        for(int j:c[i])
            fout<<j<<' ';
        fout<<'\n';
    }
    return 0;
}