#include <bits/stdc++.h>
int main() {
  int A;
  int max = 0;
  scanf("%d", &A);
  int x = 1;
  int y = A - 1;
  for (; x < A; x++, y--) {
    if (max < x * y) max = x * y;
  }
  printf("%d\n", max);
  return 0;
}
