#include <bits/stdc++.h>

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

std::vector<std::vector<int>>graph;
std::vector<std::vector<int>>ans;

int lowt[100001];
int disc[100001];
std::stack<int>st;

bool in_componenta[100001];

void tarzan(int nod)
{
    static int timer = 0;
    disc[nod] = lowt[nod] = ++timer;
    in_componenta[nod] = true;
    st.push(nod);

    for(int neigh : graph[nod])
    {
        if(disc[neigh] == -1)
        { /// nu a fost in nicio componenta pana acum
            tarzan(neigh);

            lowt[nod] = std::min(lowt[neigh], lowt[nod]);
        }
        else if(in_componenta[neigh] == true)
        {
            lowt[nod] = std::min(lowt[neigh], lowt[nod]);
        }
    }

    if(lowt[nod] == disc[nod])
    {
        std::vector<int>bag;
        int top;
        do
        {
            top = st.top();
            in_componenta[top] = false;
            bag.push_back(top);
            st.pop();

        }while(top != nod);
        ans.push_back(bag);
    }
}
int main()
{
    int n, m;
    fin >> n >> m;
    graph.resize(n + 1);

    for(int i = 1; i <= m; i++)
    {
        int a, b;
        fin >> a >> b;
        graph[a].push_back(b);
    }

    for(int i = 1; i <= n; i++)
    {
        disc[i] = -1;
    }

    for(int i = 1; i <= n; i++)
    {
        if(disc[i] == -1)
            tarzan(i);
    }
    fout << ans.size() << '\n';
    for(int i = 0; i < ans.size(); i++, fout << '\n')
        for(int j = 0; j < ans[i].size(); j++)
            fout << ans[i][j] << ' ';
}