#include<cstdio>
#include<vector>
#include<algorithm>
#include<iostream>
#include<cassert>
#include<cstring>
#include<queue>
#include<stack>
#include<map>
#include<set>
#include<string>
using namespace std;
typedef pair<int,int>pint;
typedef vector<int>vint;
#define pb push_back
#define mp make_pair
#define rep(i,n) for(int i=0;i<(n);i++)
template<class T,class U>void chmin(T &t,U f){if(t>f)t=f;}
template<class T,class U>void chmax(T &t,U f){if(t<f)t=f;}

int main(){
    int D;cin>>D;

    int ma=0;


    for(int i=1;D-i*2>1;i++){
        int a=i,b=(D-i*2)/2;
        chmax(ma,a*b);
    }

    cout<<ma<<endl;

    return 0;
}