#include<bits/stdc++.h>
using namespace std;
#define in cin
#define out cout

ifstream f ("ctc.in");
ofstream g ("ctc.out");

int const MAXSIZE = 100010;

int n, m, x, y, k, h;
vector<int> graph[MAXSIZE];
vector<int> revers[MAXSIZE];
int viz[MAXSIZE];
stack<int> st;
vector<int> sol[MAXSIZE];

int DFS(int node) {
    viz[node]++;
    for (int i = 0; i < graph[node].size(); i++) {
        if (viz[graph[node][i]] == 0) {
            DFS(graph[node][i]);
        }
    }
    st.push(node);
}

int df(int node) {
    viz[node]++;
    for (int i = 0; i < revers[node].size(); i++) {
        if (viz[revers[node][i]] == 0) {
            df(revers[node][i]);
        }
    }
    sol[k].push_back(node);
}

int solve () {
    for (int i = 1; i <= n; i++) {
        if (viz[i] == 0) {
            DFS(i);
        }
    }

    for (int i = 1; i <= n; i++)
        viz[i] = 0;

    while (!st.empty()) {
        //out << st.top() << endl;
        if (viz[st.top()] == 0) {
            df(st.top());
            k++;
        }
        st.pop();
    }

    out << k << endl;
    for(int i = 0; i <= k; i++) {
        for (int j = 0; j < sol[i].size(); j++) {
            out << sol[i][j] << " ";
        }
        out << endl;
    }
}


int main () {
    in >> n >> m;
    for (int i = 1; i <= m; i++) {
        in >> x >> y;
        graph[x].push_back(y);
        revers[y].push_back(x);
    }
    solve();

}