#include <bits/stdc++.h>
using namespace std;
int n, ans;
int f[1000];
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++)
    for (int j = 1; j <= n; j++) {
      if (i + j - 1 <= n) {
        for (int k = j; k <= i + j - 1; k++) f[k]++;
      }
    }
  for (int i = 1; i <= n; i++) ans = max(ans, f[i]);
  printf("%d", ans);
  return 0;
}
