#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, ans = 0, k = 0, l = 0;
  cin >> n;
  for (int i = 1; i <= n; i++) {
    k = n - i + 1;
    l = n;
    while (k != 0) {
      k -= l / i;
      if (l % i == 0)
        l -= 2;
      else
        l -= 1;
      ans++;
    }
  }
  cout << ans;
}
