#include <bits/stdc++.h>
#define dim int(1e5)+5
using namespace std;
ifstream f("ctc.in");
ofstream g("ctc.out");
int n,m,nivel,comp,vf;
bool seen[dim];
int low[dim],st[dim],lvl[dim];
vector <int> graph[dim],ans[dim];
void Read()
{
    f>>n>>m;
    for(int i=1;i<=m;++i)
    {
        int x,y;
        f>>x>>y;
        graph[x].push_back(y);
    }
}
void Dfs(int node)
{
    st[++vf]=node;
    lvl[node]=low[node]=++nivel;
    seen[node]=1;
    for(int i=0;i<graph[node].size();++i)
    {
        int son=graph[node][i];
        if(!lvl[son])
        {
            Dfs(son);
            low[node]=min(low[node],low[son]);
        }
        else
            if(seen[son])low[node]=min(low[node],low[son]);
    }
    if(low[node]==lvl[node])
    {
        ++comp;
        do
        {
            ans[comp].push_back(st[vf]);
            seen[st[vf]]=0;
            --vf;
        }while(vf&&st[vf+1]!=node);
    }
}
void Solve()
{
    for(int i=1;i<=n;++i)
        if(!lvl[i])
        Dfs(i);
    g<<comp<<'\n';
    for(int i=1;i<=comp;++i)
    {
        for(int j=0;j<ans[i].size();++j)
            g<<ans[i][j]<<" ";
        g<<'\n';
    }
}
int main()
{
    Read();
    Solve();
    return 0;
}