#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  while (cin >> n) {
    if (n % 2 == 0) {
      cout << 2 * n - n / 2 << endl;
    } else {
      cout << n / 2 + (n - n / 2) + n / 2 << endl;
    }
  }
}
