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

namespace ConsoleApp188
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] str = (Console.ReadLine().Split());
            long a=long.Parse(str[0]);
            long b = long.Parse(str[1]);
            long n = long.Parse(str[2]);
            long m = long.Parse(str[3]);
            long e = 0;
            if (a / n >= b )
            {
                while (a - e*n >= b + e)
                {
                    e += 1;
                }
                Console.WriteLine(a - e * n);
            }
            else
            {
                while (b - e * m >= a + e)
                {
                    e += 1;
                }
                Console.WriteLine(b - e * m);
            }
            

        }
    }
}