#include <bits/stdc++.h>
using namespace std;
int x[105] = {0, 1, 2};
int main() {
  int n;
  scanf("%d", &n);
  if (n & 1) {
    for (int i = 3; i <= n; i += 2) {
      x[i] = i + x[i - 2];
    }
  } else {
    for (int i = 4; i <= n; i += 2) {
      x[i] = i + x[i - 2];
    }
  }
  printf("%d", x[n]);
  return 0;
}
