#include <fstream>
#include <vector>

using namespace std;

vector<int> L[100005];
vector<int> G[100005];

int sol[100005];
bool viz[100005];

vector<int> q;
int k;
vector<int> s[100005];

void df(int x) {
    viz[x] = true;
    for(int i = 0; i < L[x].size(); i ++) {
        if(!viz[L[x][i]])
            df(L[x][i]);
    }
    q.push_back(x);
}

void dfT(int x) {
    sol[x] = k;
    for(int i = 0; i < G[x].size(); i ++) {
        if(!sol[G[x][i]])
            dfT(G[x][i]);
    }
}

int main()
{
    ifstream f("ctc.in");
    ofstream g("ctc.out");

    int n, m, x, y;
    f >> n >> m;
    for(int i = 1; i <= m; i ++) {
        f >> x >> y;
        L[x].push_back(y);
        G[y].push_back(x);
    }

    for(int i = 1; i <= n; i ++)
        if(!viz[i])
            df(i);

    for(; q.size(); q.pop_back()) {
        if(!sol[q.back()]) {
            k ++;
            dfT(q.back());
        }
    }

    for(int i = 1; i <= n; i ++) {
        s[sol[i]].push_back(i);
    }

    g << k << "\n";
    for(int i = 1; i <= k; i ++) {
        for(int j = 0; j < s[i].size(); j ++)
            g << s[i][j] << " ";
        g << "\n";
    }
    return 0;
}