#include <bits/stdc++.h>
using namespace std;
int A[110];
int main() {
  int n;
  scanf("%d", &n);
  A[1] = 1;
  A[2] = 2;
  for (int i = 3; i <= n; i++) A[i] = A[i - 2] + i;
  printf("%d\n", A[n]);
  return 0;
}
