#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-9;
int fx[] = {-1, 1, 0, 0, -1, -1, 1, 1};
int fy[] = {0, 0, -1, 1, -1, 1, -1, 1};
int main() {
  int a[110];
  a[0] = 0, a[1] = 1, a[2] = 2, a[3] = 4;
  for (int i = 4; i <= 110; i++) {
    a[i] = i + a[i - 2];
  }
  int n;
  cin >> n;
  cout << a[n] << endl;
  return 0;
}
