#include <bits/stdc++.h>
using namespace std;
ifstream fin ("ctc.in");
ofstream fout ("ctc.out");
const int Nmax = 100005;
vector < int > L[Nmax] , G[Nmax] , sol[Nmax];
int timp[Nmax] , k , n , m , cc;
bool viz[Nmax];
void DFST(int varf)
{
    viz[varf] = true;
    for(auto i : L[varf])
        if(!viz[i])
            DFST(i);
    ++k;
    timp[k] = varf;
}
void DFS_Solve(int varf)
{
    viz[varf] = true;
    for(auto i : G[varf])
        if(!viz[i])
            DFS_Solve(i);
    sol[cc] . push_back(varf);
}
int main()
{
    int x , y;
    fin >> n >> m;
    for(int i = 1 ; i <= m ; i++)
    {
        fin >> x >> y;
        L[x] . push_back(y);
        G[y] . push_back(x);
    }
    for(int i = 1 ; i <= n ; i++)
        if(!viz[i])
            DFST(i);
    for(int i = 1 ; i <= n ; i++)
        viz[i] = false;
    for(int i = k ; i >= 1 ; i--)
        if(!viz[timp[i]])
    {
        ++cc;
        DFS_Solve(timp[i]);
    }
    fout << cc << "\n";
    for(int pas = 1 ; pas <= cc ; pas++)
    {
        for(auto i : sol[pas])
            fout << i << " ";
        fout << "\n";
    }
    fin.close();
    fout.close();
    return 0;
}