#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  if (n == 1)
    cout << 1;
  else if (n == 2)
    cout << 2;
  else if (n == 3)
    cout << 4;
  else {
    int c = 0;
    int k = n;
    int a[n + 2];
    for (int i = 1; i <= k; i++) a[i] = n--;
    n = k;
    a[n] -= 1;
    n--;
    c++;
    while (n > k / 2) {
      c += 2;
      a[n] -= 2;
      a[k - n] -= 2;
      n--;
    }
    for (int i = k / 2 + 1; i <= k; i++) c += a[i];
    for (int i = 1; i <= k / 2; i++) c += i;
    cout << c;
  }
}
