#include <bitset>
#include <fstream>
#include <vector>
#include <stack>

#define NMAX 100001

using namespace std;

vector<int> G[NMAX], comp(NMAX), level(NMAX);
vector<vector<int>> sol;
bitset<NMAX> inStack;
stack<int> st;
int n,m,lev;

void dfs(int nod)
{
    comp[nod] = level[nod] = ++lev;
    st.push(nod);
    inStack[nod] = 1;
    for (int it : G[nod])
        if (!comp[it])
        {
            dfs(it);
            level[nod] = min(level[nod], level[it]);
        }
        else if (inStack[it])
        {
            level[nod] = min(level[nod], level[it]);
        }
    if (comp[nod] == level[nod])
    {
        vector<int> lsol;
        lsol.push_back(nod);
        while (st.top() != nod)
        {
            lsol.push_back(st.top());
            st.pop();
        }
        st.pop();
        sol.push_back(lsol);
    }
}


int main()
{
    inStack.reset();
    ifstream fin("ctc.in");
    fin >> n >> m;
    int x, y;
    for (int i = 0; i<m; i++)
    {
        fin >> x >> y;
        G[x].push_back(y);
    }
    fin.close();
    
    for (int i = 0; i < n; i++)
        if (!comp[i]) dfs(i);
    
    ofstream fout("ctc.out");
    fout << sol.size() << endl;
    for (int i = 0; i < sol.size(); i++)
    {
        for (int nod : sol[i])
            fout << nod << " ";
        fout << endl;
    }
    fout.close();
    
    return 0;
}