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

using namespace std;

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

const int nmax=100000;

vector <int> g[nmax+1];

int low[nmax+1],lvl[nmax+1],l;

bool u[nmax+1];

stack <int> s;

vector < vector <int> > sol;

void dfs(int x){
    ++l;
    lvl[x]=l;
    low[x]=l;
    u[x]=1;
    s.push(x);
    for(int i=0;i<int(g[x].size());i++){
        int xn=g[x][i];
        if(lvl[xn]==0){
            dfs(xn);
            if(low[x]>low[xn]){
                low[x]=low[xn];
            }
        }else if(u[xn]==1){
            if(low[x]>low[xn]){
                low[x]=low[xn];
            }
        }
    }
    if(lvl[x]==low[x]){
        int nsol=sol.size()+1;
        sol.resize(nsol);
        sol[nsol-1].resize(0);
        while(u[x]==1){
            int aux=s.top();
            s.pop();
            u[aux]=0;
            sol[nsol-1].push_back(aux);
        }
    }
}

int main(){
    int n,m;
    fin>>n>>m;
    for(int i=1;i<=m;i++){
        int x,y;
        fin>>x>>y;
        g[x].push_back(y);
    }
    for(int i=1;i<=n;i++){
        if(lvl[i]==0){
            dfs(i);
        }
    }
    fout<<sol.size()<<"\n";
    for(int i=0;i<int(sol.size());i++){
        for(int j=0;j<int(sol[i].size());j++){
            fout<<sol[i][j]<<" ";
        }
        fout<<"\n";
    }
    return 0;
}