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

#define REP(i, n) for(int i=0; i<(n); i++)
#define int long long

int L;
signed main()
{
    cin >> L;
    int k = 3;
    int ans = 0;
    while(k <= L) {
        ans += L - k + 1;
        k += 2;
    }
    cout << ans << endl;
    return 0;
}