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

namespace Data_Types_Variables
{
    class Program
    {
        static void Main(string[] args)
        {
            int fisrtNum = int.Parse(Console.ReadLine());
            int secondNum = int.Parse(Console.ReadLine());
            int thirdNum = int.Parse(Console.ReadLine());
            int fourthNum = int.Parse(Console.ReadLine());

            int total = 0;
            total = (fisrtNum + secondNum) / thirdNum * fourthNum;
            
            Console.WriteLine($"{total}");

        }
    }
}