#include <bits/stdc++.h>

using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
int n,m;
vector<int> g[100005],gt[100005];
stack <int> st;
void citire(){
    fin>>n>>m;
    for(int i=1;i<=m;i++){
        int x,y;
        fin>>x>>y;
        g[x].push_back(y);
        gt[y].push_back(x);
    }
}
int viz[100005];
void dfs1(int nod){
    viz[nod]=1;
    for(auto vecin:g[nod]){
        if(!viz[vecin])
            dfs1(vecin);
    }
    st.push(nod);
}
int nrcomp;
vector <int> result[100005];
void dfs2(int nod){
    viz[nod]=2;
    result[nrcomp].push_back(nod);
    for(auto vecin:gt[nod]){
        if(viz[vecin]==1)
            dfs2(vecin);
    }
}
void rezolvare(){
    for(int i=1;i<=n;++i){
        if(!viz[i])
            dfs1(i);
    }
    while(!st.empty()){
        int nod=st.top();
        if(viz[nod]==1){
            nrcomp++;
            dfs2(nod);
        }
        st.pop();
    }
}
void sortare(){
    for(int i=1;i<=nrcomp;++i){
        sort(result[i].begin(),result[i].end());
    }
}
int main()
{
    citire();
    rezolvare();
    sortare();
    fout<<nrcomp<<endl;
    for(int i=1;i<=nrcomp;++i,fout<<endl){
        for(auto el:result[i])
            fout<<el<<" ";
    }
    return 0;
}