#include <bits/stdc++.h>
using namespace std;
int f[109];
int main() {
  int n;
  cin >> n;
  f[1] = 1;
  f[2] = 2;
  f[3] = 4;
  f[4] = 6;
  for (int i = 5; i <= n; i++) {
    f[i] = 2 * f[i - 1] - f[i - 3] * 2 + f[i - 4];
  }
  cout << f[n] << endl;
  return 0;
}
