#include <bits/stdc++.h>

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

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