#include <bits/stdc++.h>

using namespace std;

int main() {

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

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

    int cnt = 0;
    vector<bool> onStack(n + 1);
    stack<int> st;
    vector<vector<int>> scc;
    vector<int> id(n + 1), low(n + 1);

    function<void(int)> dfs = [&](int node) {
        low[node] = id[node] = cnt++;
        onStack[node] = true;
        st.push(node);
        for(int son : g[node]) {
            if(!id[son]) {
                dfs(son);
            }
            if(onStack[son]) {
                low[node] = min(low[node], low[son]);
            }
        }
        if(id[node] == low[node]) {
            scc.push_back({});
            while(1) {
                int v = st.top();
                scc.back().push_back(v);
                st.pop();
                onStack[v] = false;
                if(node == v) { break; }
            }
        }
    };

    dfs(1);
    
    out << (int)scc.size() << '\n';
    for(int i = 0; i < (int)scc.size(); i++) {
        for(int node : scc[i]) {
            out << node << ' ';
        }
        out << '\n';
    }


    return 0;
}