#include<iostream>
#include<fstream>
#include<vector>
#include<stack>
#define N 100010
using namespace std;

ifstream f("ctc.in");
ofstream o("ctc.out");

int id=0,n,m,cc=0,low[N],ids[N];
bool onStack[N];
vector <int> v[N],ctc[N];
stack <int> S;
void citire(){
    f>>n>>m; int i,x,y;
    for(i=1;i<=m;i++){
        f>>x>>y;
        v[x].push_back(y);
    }
}
void dfs(int k){
    ids[k]=low[k]=++id;
    S.push(k); int i,nv;
    onStack[k]=1;
    for(i=0;i<v[k].size();i++){
        nv=v[k][i];
        if(!ids[nv]){
            dfs(nv);
            low[k]=min(low[k],low[nv]);
        }
        else if(onStack[nv]) low[k]=min(low[k],low[nv]);
    }
    if(ids[k]==low[k]){
        cc++;
        while(1){
            ctc[cc].push_back(S.top());
            onStack[S.top()]=0;
            if(S.top()==k){
                S.pop();
                return;
            }
            S.pop();
        }
    }
}
int main(){
    citire();
    int i,j;
    for(i=1;i<=n;i++)
        if(!ids[i])
            dfs(i);
    o<<cc<<'\n';
    for(i=1;i<=cc;i++){
        for(j=0;j<ctc[i].size();j++)
            o<<ctc[i][j]<<" ";
        o<<'\n';
    }
    o.close();
    f.close();
}