#include <bits/stdc++.h>
using namespace std;
int arr[105], Max;
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n; i++) {
    for (int j = 1; j + i <= n; j++) {
      for (int k = j; k <= j + i; k++) {
        arr[k]++;
      }
    }
  }
  for (int i = 1; i <= n; i++) Max = max(Max, arr[i]);
  printf("%d", Max);
  return 0;
}
