#include <bits/stdc++.h>
using std::abs;
using std::cin;
using std::cout;
using std::endl;
using std::map;
using std::max;
using std::min;
using std::ostream_iterator;
using std::pair;
using std::search;
using std::set;
using std::string;
using std::vector;
int main() {
  int n;
  cin >> n;
  cout << n + n / 2 << endl;
  return 0;
}
