#include <bits/stdc++.h>
int main() {
  int a[105];
  int i = 0;
  a[1] = 1;
  a[2] = 2;
  a[3] = 4;
  for (i = 4; i <= 100; i++) {
    a[i] = i + a[i - 2];
  }
  int n;
  scanf("%d", &n);
  printf("%d", a[n]);
  return 0;
}
