#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  vector<long long int> a(102);
  a[0] = 0;
  a[1] = 1;
  a[2] = 2;
  int k = 2;
  for (int i = 3; i <= 100; i += 2) {
    a[i] = a[i - 1] + k;
    a[i + 1] = a[i] + k;
    k++;
  }
  int n;
  cin >> n;
  cout << a[n];
}
