#include <bits/stdc++.h>
using namespace std;
using vint = vector<long long>;
using pint = pair<long long, long long>;
using vpint = vector<pint>;
template <typename A, typename B>
inline void chmin(A& a, B b) {
  if (a > b) a = b;
}
template <typename A, typename B>
inline void chmax(A& a, B b) {
  if (a < b) a = b;
}
template <class A, class B>
ostream& operator<<(ostream& ost, const pair<A, B>& p) {
  ost << "{" << p.first << "," << p.second << "}";
  return ost;
}
template <class T>
ostream& operator<<(ostream& ost, const vector<T>& v) {
  ost << "{";
  for (long long i = 0; i < v.size(); i++) {
    if (i) ost << ",";
    ost << v[i];
  }
  ost << "}";
  return ost;
}
signed main() {
  long long a, p;
  p += a * 3;
  cout << p / 2 << endl;
  return 0;
}
