#include <iostream>
#include <fstream>
#include <queue>
#include <stack>
using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
vector <int > G1[50005],G2[50005],v[50005];
stack < int > s ;
int n,m,x,y,vis1[50005],vis2[50005],p,nr;
void dfs1(int k)
{ vis1[k]=1;
for(int i : G1[k])
{
    if(!vis1[i])
        dfs1(i);
}
s.push(k);
}
void dfs2(int k)
{vis2[k]=1;
    for(int i : G2[k])
    {
     if(!vis2[i])
        dfs2(i);
    }
    v[nr].push_back(k);
}
int main()
{f>>n>>m;
for(int i=1;i<=m;++i)
{
f>>x>>y;
    G1[x].push_back(y);
    G2[y].push_back(x);
}
for(int i=1;i<=n;++i)
{
    if(!vis1[i])
        dfs1(i);
}
while(!s.empty())
{
    p=s.top();
    if(!vis2[p])
    {
        nr++;
        dfs2(p);
    }
        s.pop();
}
g<<nr<<'\n';
for(int i=1;i<=nr;++i)
{
    for(int j :v[i])
        g<<j<<" ";
    g<<'\n';
}
    return 0;
}