#include <fstream>
#include <vector>
#include <stack>
#define maxSize 100005
using namespace std;

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

vector<int> nodes[maxSize],transpus[maxSize],ctc[maxSize];
int n,m,k,visited[maxSize];
stack<int> s;

void read(){
    fin>>n>>m;
    int x,y;
    for(int i=0; i<m; i++){
        fin>>x>>y;
        nodes[x].push_back(y);
        transpus[y].push_back(x);
    }
}

void dfs(int node){
    visited[node]=1;
    for(auto it: nodes[node])
        if(visited[it]==0)
            dfs(it);
    s.push(node);
}

void dfs2(int node,int k){
    visited[node]=-1;
    for(auto it:transpus[node])
        if(visited[node]>0)
             dfs2(it,k);
    ctc[k].push_back(node);
}

void da(){
    for(int i=1; i<=n; i++)
        if(visited[i]==0)
            dfs(i);
}

void da2(){
    while(!s.empty()){
        int v=s.top();
        s.pop();
        if(visited[v]<0)
            continue;
        k++;
        dfs2(v,k);
    }
}

void print(){
    fout<<k<<"\n";
    for(int i=1; i<=k; i++){
        for(auto it:ctc[i])
            fout<<it<<" ";
        fout<<"\n";
    }
}

int main()
{
    read();
    da();
    da2();
    print();
    return 0;
}