#include <iostream>
#include <fstream>
#include <vector>
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");

vector <int> G[100002];
vector <int> H[100002];
vector <int> A[100002];
int n,m,x,y,S[100001],D[100001],c;

void dfs_succ(int v, int c)
{
    S[v] = c;
    for(int i : G[v])
        if(!S[i]) dfs_succ(i, c);
}

void dfs_pred(int v , int c)
{
    D[v] = c;
    for(int i : H[v])
        if(!D[i]) dfs_pred(i, c);
}

int main()
{
    fin >> n >> m;
    for(int i = 1 ; i <= m ; i++)
    {
        fin >> x >> y;
        G[x].push_back(y);
        H[y].push_back(x);
    }

    for(int i = 1 ; i <= n ; i++)
    {
        if(!S[i])
        {
            c++;
            dfs_succ(i, c);
            dfs_pred(i, c);
            for(int i=1;i<=n;i++)
                if(S[i] != D[i])
                    S[i]=D[i]=0;
        }

        A[c].push_back(i);
    }
    fout<<c<<endl;;
    for(int i=1;i<=c;i++)
    {
        for(int x:A[i])
            fout<<x<<" ";
        fout<<endl;
    }
    return 0;
}