#include <bits/stdc++.h>
#define N 100005
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
int n,m,nrc;
vector<int>g[N],gt[N],ctc[N],s;
bitset<N>viz;
void DFS1(int k)
{
    viz[k]=1;
    for(int i:g[k])
        if(!viz[i]) DFS1(i);
    s.push_back(k);
}
void DFS2(int k)
{
    viz[k]=1;
    for(int i:gt[k])
        if(!viz[i]) DFS2(i);
    ctc[nrc].push_back(k);
}
int main()
{
    int i,x,y;
    fin>>n>>m;
    while(m--) fin>>x>>y,g[x].push_back(y),gt[y].push_back(x);
    for(i=1;i<=n;i++)
        if(!viz[i]) DFS1(i);
    reverse(s.begin(),s.end());
    viz.reset();
    for(auto i:s)
        if(!viz[i])
    {
        ++nrc;
        DFS2(i);
    }
    fout<<nrc<<"\n";
    for(i=1;i<=nrc;i++)
    {
        for(auto x:ctc[i]) fout<<x<<" ";
        fout<<"\n";
    }
    return 0;
}