#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using ull = unsigned long long;
using ld = long double;
template<class t> using vc = vector<t>;
template<class t> using vvc = vc<vc<t>>;
using pi = pair<int,int>;
using vi = vc<int>;
using vvi = vvc<int>;

#define rep(i,a,b) for (ll i = a; i < b; i++)
#define irep(i,a,b) for (int i = a; i > b; i--)
#define print(n) cout << n << endl
#define rup(a,b) (a+b-1)/b
#define input(A,N) rep(i,0,N) cin>>A[i];


int main(){
    cout << fixed << setprecision(15);
    
    int D = 0;
    ll ans = 0;
    rep(i,0,D){
        ll a = (D-2*i)/2;
        ans = max(ans,i*a);
    }

    print(ans);
    
    //system("pause");
    return 0;
}