#include <bits/stdc++.h>
using namespace std;
void solve() {
  long long n;
  cin >> n;
  cout << 3 * n / 2 << "\n";
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long t;
  t = 1;
  while (t--) {
    solve();
  }
  return 0;
}
