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

using namespace std;

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

vector <int> l[100010],c[100010];
int n,m,ctc,g,niv[100010],low[100010],x,y,i,j;
stack <int> s;

void dfs (int nod) {

    niv[nod]=low[nod]=++g;
    s.push(nod);
    for (int i=0;i<l[nod].size();i++) {
        int fiu=l[nod][i];
        if (!niv[fiu])
            dfs(fiu);
        if (niv[fiu]>0)
            low[nod]=min(low[nod],low[fiu]);
    }
    if (niv[nod]<=low[nod]) {
        ctc++;
        do{
            x=s.top();
            c[ctc].push_back(x);
            niv[x]*=-1;
            s.pop();
        }while (x!=nod );
    }
}

int main () {

    fin>>n>>m;
    while (m--) {
        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<c[i].size();j++)
            fout<<c[i][j]<<" ";
        fout<<"\n";
    }

    return 0;
}