#include <bits/stdc++.h>

using namespace std;

ifstream fin ("ctc.in");
ofstream fout ("ctc.out");

void usain_bolt()
{
    ios::sync_with_stdio(false);
    fin.tie(0);
}

const int N = 1e5 + 5;

vector < int > a[N];
vector < vector < int > > sol;

int disc[N], temp, low[N], in_stack[N];
stack < int > st;

void dfs(int k)
{
    disc[k] = low[k] = ++temp;
    in_stack[k] = true;
    st.push(k);
    for(auto v : a[k]) {
        if(disc[v] == 0) {
            dfs(v);
            low[k] = min(low[k], low[v]);
        }
        else if(in_stack[v] == true) {
            low[k] = min(low[k], low[v]);
        }
    }
    if(low[k] == disc[k]) {
        vector < int > add;
        int node = k;
        do {
            node = st.top();
            add.push_back(node);
            in_stack[node] = false;
            st.pop();
        }
        while(node != k);
        sol.push_back(add);
    }
}

int main()
{
    usain_bolt();

    int n, m;

    fin >> n >> m;
    for(int i = 1; i <= m; ++i) {
        int x, y;

        fin >> x >> y;
        a[x].push_back(y);
    }
    for(int i = 1; i <= n; ++i) {
        if(disc[i] == false) {
            dfs(i);
        }
    }
    fout << (int) sol.size() << "\n";
    for(auto v : sol) {
        for(auto w : v) {
            fout << w << " ";
        }
        fout << "\n";
    }
    return 0;
}