#include <iostream>
#include <fstream>
#include <vector>
#include <stack>
using namespace std;

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

int n, m, index, nr;
int idx[100001], lowlink[100001];
bool in_s[100001];
vector<int> gf[100001], afis[100001];
stack<int> s;

void tarjan(int n) {
    in_s[n] = true;
    s.push(n);
    idx[n] = lowlink[n] = index++;

    for (auto vecin : gf[n]) {
        if (idx[vecin] == -1)
            tarjan(vecin);
        if (in_s[vecin])
            lowlink[n] = min(lowlink[n], lowlink[vecin]);
    }

    if (lowlink[n] == idx[n]) {
        while (!s.empty()) {
            int aux = s.top();
            s.pop();
            afis[nr].push_back(aux);
            in_s[aux] = false;
            lowlink[aux] = idx[n];
            if (aux == n)
                break;
        }
        nr++;
    }
}

int main()
{
    fin >> n >> m;
    for (int i = 1; i <= m; i++) {
        int x, y;
        fin >> x >> y;
        gf[x].push_back(y);
    }

    for (int i = 1; i <= n; i++)
        idx[i] = -1;
    for (int i = 1; i <= n; i++)
        if (idx[i] == -1)
            tarjan(i);

    fout << nr << "\n";
    for (int i = 0; i < nr; i++) {
        for (auto tmp : afis[i])
            fout << tmp << " ";
        fout << "\n";
    }
    return 0;
}