using System;
using System.Collections.Generic;
using System.Linq;

// https://yukicoder.me/problems/no/2558
class Program
{
    static string InputPattern = "InputX";

    static List<string> GetInputList()
    {
        var WillReturn = new List<string>();

        if (InputPattern == "Input1") {
            WillReturn.Add("3 5 1 2");
            //7
        }
        else if (InputPattern == "Input2") {
            WillReturn.Add("1 3000 0 0");
            //0
        }
        else if (InputPattern == "Input3") {
            WillReturn.Add("998 2443 5 3");
            //2203589
        }
        else {
            string wkStr;
            while ((wkStr = Console.ReadLine()) != null) WillReturn.Add(wkStr);
        }
        return WillReturn;
    }

    static void Main()
    {
        List<string> InputList = GetInputList();
        long[] wkArr = InputList[0].Split(' ').Select(pX => long.Parse(pX)).ToArray();
        long A = wkArr[0];
        long B = wkArr[1];
        long a = wkArr[2];
        long b = wkArr[3];

        for (long I = 0; I <= A * B; I++) {
            if (I % A == a && I % B == b) {
                Console.WriteLine(I);
                return;
            }
        }
    }
}