#include <bits/stdc++.h>

using namespace std;
#ifdef HOME
ifstream fin("ciorna.in");
ofstream fout("ciorna.out");
#else
ifstream fin("ctc.in");
ofstream fout("ctc.out");
#endif
const int N = 1e5;
vector <vector <int>> scc;
vector <int> g[N + 5];
stack <int> st;
int low[N + 5], id[N + 5], timer;
bool onstack[N + 5];

void dfs(int u) {
    onstack[u] = true;
    st.push(u);
    low[u] = id[u] = ++timer;
    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]) {
        scc.push_back({u});
        while(st.top() != u) {
            onstack[st.top()] = false;
            scc.back().push_back(st.top());
            st.pop();
        }
        st.pop();
        onstack[u] = false;
    }
}

int main()
{
    int n, m, u, v;
    fin >> n >> m;
    for(int i = 1; i <= m; i++)
        fin >> u >> v,
        g[u].push_back(v);
    for(int i = 1; i <= n; i++) if(!id[i])
        dfs(i);
    fout << scc.size() << "\n";
    for(auto& v : scc) {
        for(int u : v)
            fout << u << " ";
        fout << "\n";
    }
    return 0;
}