#include <bits/stdc++.h>
using namespace std;
const int inf = 0x3f3f3f3f;
const long long __64inf = 0x3f3f3f3f3f3f3f3f;
const int MAX = 1e5 + 5;
const int Mod = 1e9 + 7;
long long dp1[MAX], dp2[MAX];
int main() {
  long long a, b;
  cout << (a * 3 + b) / 2 << endl;
  return 0;
}
