#include <bits/stdc++.h>
using namespace std;
constexpr long long int INF = std::numeric_limits<long long int>::max();
constexpr long long int MOD = 1000000007;
constexpr long long int SIZE = 100100;
void solve() {
  long long int a;
  cin >> a;
  cout << a * 3 / 2 << endl;
}
signed main() {
  solve();
  return 0;
}
