#include <bits/stdc++.h>

using namespace std;
using vit = vector<int>::reverse_iterator;

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

const int NMAX = 1e5 + 1;

int n, m, idx[NMAX], lowlink[NMAX], ctcs, index;
vector<int> v[NMAX];
vector<int> ctc[NMAX];
bool inStack[NMAX];
stack<int> stk;

void tarjan(int node) {
    ++index;
    idx[node] = index;
    lowlink[node] = index;
    stk.push(node);
    inStack[node] = 1;
    for (const int& x: v[node]) {
        if (!idx[x]) {
            tarjan(x);
            lowlink[node] = min(lowlink[node], lowlink[x]);
        }
        else if (inStack[x]) {
            lowlink[node] = min(lowlink[node], lowlink[x]);
        }
    }
    if (idx[node] == lowlink[node]) {
        int x;
        ++ctcs;
        do {
            x = stk.top();
            stk.pop();
            inStack[x] = 0;
            ctc[ctcs].push_back(x);
        } while (x != node);
    }
}

int main()
{
    fin >> n >> m;
    for (int x, y; m; --m) {
        fin >> x >> y;
        v[x].push_back(y);
    }
    for (int i = 1; i <= n; ++i) {
        if (!idx[i]) {
            tarjan(i);
        }
    }
    fout << ctcs << '\n';
    for (int i = 1; i <= ctcs; ++i) {
        for (const int& x: ctc[i])
            fout << x << ' ';
        fout << '\n';
    }
    return 0;
}