#include<bits/stdc++.h>
using namespace std;
using Int = long long;
template<typename T1,typename T2> inline void chmin(T1 &a,T2 b){if(a>b) a=b;}
template<typename T1,typename T2> inline void chmax(T1 &a,T2 b){if(a<b) a=b;}

//INSERT ABOVE HERE
signed main(){
  Int d;
  cin>>d;
  Int ans=0;  
  for(Int x=0;x*2<=d;x++)
    for(Int y=0;(x+y)*2<=d;y++)
      chmax(ans,x*y);
  cout<<ans<<endl;
  return 0;
}