#include <bits/stdc++.h>

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

int main()
{
    #ifndef HOME
    ifstream cin("ctc.in");
    ofstream cout("ctc.out");
    #endif // HOME
    int n, m, u, v;
    cin >> n >> m;
    for(int i = 1; i <= m; i++)
        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& comp : cc) {
        for(int x : comp)
            cout << x << " ";
        cout << "\n";
    }
    return 0;
}