c#include <bits/stdc++.h> using namespace std; int main() { cin.tie(0); cout.tie(0); ios_base::sync_with_stdio(false); int N; cin >> N; if(N == 1){ cout << 0 << "\n"; return 0; } if(N % 2){ cout << N * N / 2 + 1 << "\n"; }else{ cout << N * N / 2 << "\n"; } return 0; }