#include <bits/stdc++.h>

using namespace std;

int n, m, p, post[50005];
vector<int> v[50005], vt[50005], r;
vector< vector<int> > sol;
bool ok[50005];

void df(int x)
{
    ok[x] = 1;
    for (vector<int>::iterator it = v[x].begin(); it != v[x].end(); ++it)
        if(!ok[*it]){
            ok[*it] = 1;
            df(*it);
        }
    post[++p] = x;
}

void dft(int x)
{
    r.push_back(x);
    ok[x] = 0;
    for (vector<int>::iterator it = vt[x].begin(); it != vt[x].end(); ++it)
        if(ok[*it]){
            ok[*it] = 0;
            dft(*it);
        }
}

int main()
{
    ifstream fin ("ctc.in");
    ofstream fout ("ctc.out");
    fin >> n >> m;
    while(m--){
        int x, y;
        fin >> x >> y;
        v[x].push_back(y);
        vt[y].push_back(x);
    }
    for (int i = 1; i <= n; ++i)
        if(!ok[i])
            df(i);
    for (int i = 1; i <= p; ++i)
        if(ok[i]){
            r.clear();
            dft(i);
            sol.push_back(r);
        }
    fout << sol.size() << "\n";
    for (vector< vector<int> >::iterator it = sol.begin(); it != sol.end(); ++it){
        for (vector<int>::iterator it2 = it->begin(); it2 != it->end(); ++it2)
            fout << *it2 << " ";
        fout << "\n";
    }
    return 0;
}