#include <fstream>
#include <vector>

using namespace std;

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

int n,m,x,y, k, i, j;
vector<int>ls[100005], ls2[100005],sol[100005];
int viz[100005], stk[100005], vf, ns;

void dfUP(int x){
    int l = ls[x].size(), y, i;
    viz[x] = 1;
    for (i = 0; i < l; i++) {
        y = ls[x][i];
        if (viz[y] == 0)
            dfUP(y);
    }
    stk[++vf] = x;
}

void dfDOWN(int x){
    int l = ls2[x].size(), y, i;
    viz[x] = n;
    for (i = 0; i < l; i++) {
        y = ls2[x][i];
        if (viz[y] == 1)
            dfDOWN(y);
    }
    sol[ns].push_back(x);
}


int main() {
    fin>>n>>m;
    while(m--) {
        fin>>x>>y;
        ls[x].push_back(y);
        ls2[y].push_back(x);
    }
    for (i = 1; i <= n; i++)
        if (viz[i] == 0)
            dfUP(i);
    for (i = n; i >= 1; i--)
        if (viz[stk[i]] != n) {
            ns++;
            dfDOWN(stk[i]);
        }
    fout<<ns<<'\n';
    for (int i=1;i<=ns;i++) {
        for (int j=0;j<sol[i].size();j++)
            fout<<sol[i][j]<<' ';
        fout<<'\n';
    }
    return 0;
}