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

string numeFisier="ctc";
ifstream fin(numeFisier+".in"); ofstream fout(numeFisier+".out");
#define cin fin
#define cout fout

#define INIT  ios_base :: sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
#define mp make_pair
#define pb push_back
#define ft first
#define sc second
#define ll long long
#define pii pair<int, int>
#define count_bits __builtin_popcount
//#define int ll


int n,m;
vector<int> g[100010];
vector<int> component[100010];

int indexArray0=0;
int indexArray[100010];
int lowlink[100010];

bool onStack[100010];
stack<int> st;
void strongConnected(int u){
    
    indexArray0++;
    indexArray[u] =indexArray0;
    lowlink[u] = indexArray0;

    st.push(u);
    onStack[u]=true;

    for(int v:g[u]){
        if(!indexArray[v]){
            strongConnected(v);
            lowlink[u]=min(lowlink[u], lowlink[v]);
        }
        else{
            if( onStack[v] ){
                lowlink[u] = min(lowlink[u], indexArray[v]);
            }
        }
    }

    if( lowlink[u]==indexArray[u] ){
        while(!st.empty() && st.top()!=u ){
            onStack[u]=false;
            component[u].pb(st.top());
            st.pop();
        }
        component[u].pb(u);
        st.pop();
    }
}


int32_t main(){
    INIT

    cin>>n>>m;
    for(int i=1,x,y; i<=m; i++){
        cin>>x>>y;
        g[x].pb(y);
    }

    for(int i=1; i<=n; i++){
        if(!indexArray[i]){
            strongConnected(i);
        }
    }

    int cnt = 0;
    for(int i=1; i<=n; i++){
        if(component[i].size()>0){
            cnt++;
        }
    }
    cout<<cnt<<"\n";
    for(int i=1; i<=n; i++){
        if(component[i].size()>0){
            for(int x:component[i]){
                cout<<x<<" ";
            }
            cout<<"\n";
        }
    }

    return 0;
}