#include <bits/stdc++.h>

using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
const int nMax = 100005;
bool viz[nMax];
int St[nMax], k, comp;
vector<int> G[nMax], Transpus[nMax], ans[nMax];
inline void Topologica(int nod) {
    viz[nod] = 1;
    for(const auto &v : G[nod]) {
        if(!viz[v]) {
            Topologica(v);
        }
    }
    St[++k] = nod;
}
inline void Invers(int nod) {
    viz[nod] = 1;
    ans[comp].push_back(nod);
    for(const auto &v: Transpus[nod]) {
        if(!viz[v]) {
            Invers(v);
        }
    }
}
int main()
{
    int n, m, x, y;
    f >> n >> m;
    for(int i = 1; i <= m; i++) {
        f >> x >> y;
        G[x].push_back(y);
        Transpus[y].push_back(x);
    }
    for(int i = 1; i <= n; i++) {
        if(!viz[i]) {
            Topologica(i);
        }
    }
    for(int i = 1; i <= n; i++) {
        viz[i] = 0;
    }
    comp = 0;
    for(int i = k; i >= 1; i--) {
        if(!viz[St[i]]) {
            comp++;
            Invers(St[i]);
        }
    }
    g << comp << "\n";
    for(int i = 1; i <= comp; i++) {
        for(const auto &x : ans[i]) {
            g << x << " ";
        }
        g << "\n";
    }
    return 0;
}