#include <bits/stdc++.h>
using namespace std;
ifstream fin("ctc.in");
ofstream fout("ctc.out");
int d[100001],n,nrc,nr,m; bool v[100001]; vector <int> a[100001],a2[100001],c[100001];

void dfs(int x){ if(!v[x]){ v[x]=1;
 for(int it : a[x]) dfs(it);
 d[++nr]=x;
 }
}

void dfs2(int x){ if(v[x]){ v[x]=0;
 for(int it : a2[x])dfs2(it);
 c[nrc].push_back(x);
 }
}
int main()
{
    fin>>n>>m; int x,y,i; while(fin>>x>>y)a[x].push_back(y),a2[y].push_back(x);

    for(i=1;i<=n;i++)dfs(i);
    for(i=n;i>=1;i--)if(v[d[i]]){nrc++; dfs2(d[i]);}

    fout<<nrc<<'\n';
    for(i=1;i<=nrc;i++){for(int it : c[i])fout<<it<<" "; fout<<'\n';}
    return 0;
}