#include <bits/stdc++.h>
using namespace std;
const long long int N = 1e9 + 100;
const int mod = 1e9 + 7, M = 1e6 + 100, se = 85 + 85;
int ans, a, b, c, d, n, m;
string s;
int main() {
  ios_base::sync_with_stdio(false), cin.tie(NULL), cout.tie(NULL);
  cin >> n;
  cout << (3 * n) / 2;
}
