#include <fstream>
#include <vector>
#include <stack>
#include <bitset>
#define DIM 100011
using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
int n,m,niv[DIM],low[DIM],gr,ctc;

vector<int> L[DIM],R[DIM];
stack<int> S;
bitset<DIM> viz,IS;

void dfs(int nod){
    int x,i;
    gr++;
    low[nod]=niv[nod]=gr;
    S.push(nod);
    viz[nod]=IS[nod]=1;
    for(i=0;i<L[nod].size();i++){
        x=L[nod][i];
        if(!viz[x]){
            dfs(x);
            low[nod]=min(low[nod],low[x]);
        }
        else if(IS[x])
                low[nod]=min(low[nod],low[x]);
    }
    if(low[nod]==niv[nod]){
        ctc++;
        do{ x=S.top(),S.pop();
            IS[x]=0;
            R[ctc].push_back(x);
        }while(x!=nod);
    }
}

int main(void){
    register int i,j,x,y;

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

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

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