#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, d[NMAX], ctcs;
vector<int> v[NMAX];
vector<int> ctc[NMAX];
bool inStack[NMAX];
stack<int> stk;

int tarjan(int node, int depth) {
    d[node] = depth;
    stk.push(node);
    inStack[node] = 1;

    for (const int& x: v[node]) {
        if (d[x] == 0) {
            d[node] = min(d[node], tarjan(x, depth + 1));
        }
        else if (inStack[x]) {
            d[node] = min(d[node], d[x]);
        }
    }

    if (d[node] == depth) {
        ++ctcs;
        int x;
        do {
            x = stk.top();
            stk.pop();
            inStack[x] = false;
            ctc[ctcs].push_back(x);
        } while (x != node);
    }

    return d[node];
}

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