#include <fstream>
#include <vector>
#include <stack>
#include <bitset>

#define DIM 100010

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

vector<int> L[DIM], R[DIM];
int g, n, m, i, x, y, ctc, j;
int niv[DIM], low[DIM];

stack<int> s;
bitset<DIM> IS;

void dfs(int nod) {
    g++;
    niv[nod] = g;
    low[nod] = g;
    s.push(nod);
    IS[nod] = 1;
    for (int i=0;i<L[nod].size();i++) {
        int x = L[nod][i];
        if (niv[x] == 0) {  //niv joak rol si de viz
            dfs(x);
            low[nod] = min(low[nod], low[x]);
        } else
            if (IS[x])
                low[nod] = min(low[nod], low[x]);

    }
    if (niv[nod] == low[nod]) {
        ctc++;
        int x;
        do {
            x = s.top();
            R[ctc].push_back(x);
            s.pop();
            IS[x] = 0;
        } while (x!=nod);
    }
}

int main() {
    fin>>n>>m;

    for (i=1;i<=m;i++) {
        fin>>x>>y;
        L[x].push_back(y);
    }

    for (i=1;i<=n;i++)
        if (!niv[i])
            dfs(i);

    fout<<ctc<<"\n";
    for (i=1;i<=ctc;i++) {
        for (j=0;j<R[i].size();j++)
            fout<<R[i][j]<<" ";
        fout<<"\n";
    }

    return 0;
}