#include <iostream>
#include <vector>
#include <stack>
#include <fstream>

using namespace std;

void be(int &n, vector<vector<int>> &adj) {
    ifstream fin("ctc.in");
    int m;
    fin >> n >> m;
    adj.resize(n+1);
    while(m--) {
        int u, v;
        fin >> u >> v;
        adj[u].push_back(v);
    }
}

vector<vector<int>> ans;

void SCC(int from, int n, vector<int> &disc, vector<int> &low, vector<bool> &onstack, vector<vector<int>> &adj, stack<int> &st, int &time) {
    disc[from]=low[from]=time;
    time++;
    onstack[from]=true;
    st.push(from);
    for(auto it : adj[from]) {
        if(disc[it]==-1) {
            SCC(it, n, disc, low, onstack, adj, st, time);
            low[from]=min(low[from], low[it]);
        } else if(onstack[it]) {
            low[from]=min(low[from], disc[it]);
        }
    }

    if(low[from]==disc[from]) {
        vector<int> comp;
        while(from!=st.top()) {
            comp.push_back(st.top());
            onstack[st.top()]=false;
            st.pop();
        }
        comp.push_back(st.top());
        onstack[st.top()]=false;
        st.pop();
        ans.push_back(comp);
    }
}

int main() {
    int n;
    vector<vector<int>> adj;
    be(n, adj);

    vector<int> disc(n+1, -1);
    vector<int> low(n+1, -1);
    vector<bool> onstack(n+1);
    stack<int> st;
    int time=0;

    for(int i=1; i<=n; i++) {
        if(disc[i]==-1) {
            SCC(i ,n, disc, low, onstack, adj, st, time);
        }
    }


    ofstream fout("ctc.out");
    fout << ans.size() << '\n';
    for(int i=0; i<ans.size(); i++) {
        for(auto it : ans[i]) {
            fout << it << ' ';
        }
        fout << '\n';
    }

    return 0;
}