#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  int n;
  cin >> n;
  int a[105], d = 1;
  a[0] = 0;
  for (int i = 1; i <= n; i++) {
    a[i] = a[i - 1] + d;
    if (i % 2 == 0) d++;
  }
  cout << a[n];
  return 0;
}
