#include <bits/stdc++.h>
#define pii pair<int,int>
#define pb push_back
#define ll long long
using namespace std;

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

const int nmax=1e5;

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

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


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

void tarjan(int nod,int pr){
    d[nod]=low[nod]=++timer;
    stk.push(nod);
    on_stack[nod]=1;
    for(int i:v[nod]){
        if(on_stack[i])
            low[nod]=min(low[nod],d[i]);
        else if(!d[i]){
            tarjan(i,nod);
            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,i);
    fout<<cnt<<'\n';
    for(int i=1;i<=cnt;i++){
        for(int j:c[i])
            fout<<j<<' ';
        fout<<'\n';
    }
    return 0;

}