using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace yukicoderTest
{
    class Program
    {
        static void Main(string[] args)
        {
            string str = Console.ReadLine();
            int n = int.Parse(str);
            double ans = 1.5 * n;
            Console.WriteLine((int)ans / 1);
        }
    }
}