import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        
        int A = sc.nextInt();
        int B = sc.nextInt();
        int a = sc.nextInt();
        int b = sc.nextInt();
        
        for (int x = 0; true; x++) {
            if (x % A == a && x % B == b) {
                System.out.println(x);
                return;
            }
        }
    }
}