int apple = 0;
int piece_apple = 0;

InputStreamReader isr = new InputStreamReader(System.in);
BufferedReader br = new BufferedReader(isr);

try {
  String str = "";
  str = br.readLine();
  br.close();
  String strs[] = str.split(" ", 2);
  apple = Integer.parseInt(strs[0]);
  piece_apple = Integer.parseInt(strs[0]);
} catch(IOException e) {
  e.printStackTrace();
}

System.out.println((3 * apple + piece_apple) / 2);