#include <bits/stdc++.h>
const int MX = 1000000007;
const long long mod = MX;
const long long MMX = (long long)MX * MX;
const long long MMN = (long long)(-MX) * MX;
using namespace std;
int n;
int get(int n) {
  if (n == 1) return 1;
  if (n == 2) return 2;
  return n + get(n - 2);
}
int main() {
  ios_base::sync_with_stdio(false);
  cin >> n;
  cout << get(n);
  return 0;
}
