import java.util.*;
import java.io.*;
class Main{
	private static final BufferedReader br =
		new BufferedReader(new InputStreamReader(System.in));
	private static final PrintWriter out =
		new PrintWriter(System.out);
	public static void main(String[] args)throws IOException{

		String[] str = br.readLine().split(" ");
		int A = Integer.parseInt(str[0]);
		int B = Integer.parseInt(str[1]);
		int a = Integer.parseInt(str[2]);
		int b = Integer.parseInt(str[3]);
		for(int i=0;;i++)
			if(i%A==a&&i%B==b){
				out.println(i);
				break;
			}

		br.close();
		out.close();
	}
}