#include <bits/stdc++.h>
using namespace std;
int n, d[101];
int main() {
  cin >> n;
  d[1] = 1;
  d[2] = 2;
  for (int i = 3; i <= n; ++i) {
    d[i] = i + d[i - 2];
  }
  cout << d[n];
  return 0;
}
