#include <bits/stdc++.h>
using namespace std;
long long MOD = 1e9 + 7, MAX = 1e18;
int main() {
  long long n, m, c, ans = 0, l = 0, k, w, sum = 0;
  map<long long, long long> mp;
  cin >> n;
  cout << (3 * n / 2);
  return 0;
}
