#include <bits/stdc++.h>

using namespace std;
const int N = 1e5;
int low[N + 5], id[N + 5];
stack <int> st;
bool onstack[N + 5];
vector <vector <int>> cc;
vector <int> g[N + 5];
int timer;
void dfs(int u) {
    low[u] = id[u] = ++timer;
    onstack[u] = true;
    st.push(u);
    for(int v : g[u]) {
        if(!id[v]) {
            dfs(v);
            low[u] = min(low[u], low[v]);
        } else if(onstack[v])
            low[u] = min(low[u], id[v]);
    }
    if(low[u] == id[u]) {
        cc.push_back({u});
        while(st.top() != u) {
            cc.back().push_back(st.top());
            onstack[st.top()] = false;
            st.pop();
        }
        onstack[u] = false;
        st.pop();
    }
}

int main()
{
    ifstream cin("ctc.in");
    ofstream cout("ctc.out");
    int n, m;
    cin >> n >> m;
    for(int i = 0; i < m; i++) {
        int u, v;
        cin >> u >> v;
        g[u].push_back(v);
    }
    for(int i = 1; i <= n; i++) if(!id[i])
        dfs(i);
    cout << cc.size() << "\n";
    for(auto& v : cc) {
        for(int x : v)
            cout << x << " ";
        cout << "\n";
    }
    return 0;
}