#include <bits/stdc++.h>
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
const int MAXN = 1e5 + 5;
int ctc;
bool viz[MAXN], viz2[MAXN];
vector <int> v[MAXN], inv[MAXN], comp[MAXN];
vector <int> sol;
void dfs1(int node){
    if(viz[node]) return;
    viz[node] = true;
    for(auto x : v[node]) dfs1(x);
    sol.push_back(node);
}
void dfs2(int node) {
    if(viz2[node]) return;
    viz2[node] = true;
    for(auto x : inv[node]) dfs2(x);
    comp[ctc].push_back(node);
}
int 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);
        inv[y].push_back(x);
    }
    for(int i = 1; i <= n; ++i)
        if(!viz[i]) dfs1(i);
    for(int i = sol.size() - 1; i >= 0 ; --i)
        if(!viz2[sol[i]]) dfs2(sol[i]), ctc ++;
    fout << ctc << '\n';
    for(int i = 0; i <= ctc; ++i){
        for(auto x : comp[i])
            fout << x << " " ;
        fout << '\n';
    }
    return 0;
}