#include <fstream>
#include <vector>
#include <stack>
using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
const int nMax = 100001, mMax = 200001;
vector<int>G[nMax];
vector<int>c[nMax];
int ids[nMax];
int low[nMax];
stack<int>S;
bool inStack[nMax];
int n, m, id, nrC;
void tarjan(int nod) {
    ids[nod] = low[nod] = ++id;
    S.push(nod);
    inStack[nod] = true;
    for (auto i : G[nod]) {
        if (!ids[i]) {
            tarjan(i);
            low[nod] = min(low[nod], low[i]);
        }
        else if (inStack[i]) {
            low[nod] = min(low[nod], ids[i]);
        }
    }
    if (ids[nod] == low[nod]) {
        nrC++;
        while (true) {
            int val = S.top();
            S.pop();
            inStack[val] = false;
            c[nrC].push_back(val);
            if (val == nod)
                break;
        }
    }
}
int main() {
    f >> n >> m;
    for (int i = 1; i <= m; ++i) {
        int x, y;
        f >> x >> y;
        G[x].push_back(y);
    }
    for (int i = 1; i <= n; ++i) {
        if (!ids[i]) {
            id = 0;
            tarjan(i);
        }
    }
    g << nrC << '\n';
    for (int i = 1; i <= nrC; ++i) {
        for (auto j : c[i])
            g << j << ' ';
        g << '\n';
    }
    return 0;
}