import java.awt.*;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;

public class Main{

    public static void main(String agr[]) throws Exception {
        FastReader sc = new FastReader();
        long cnt1=sc.nextInt(),cnt2=sc.nextInt(),x=sc.nextInt(),y=sc.nextInt();
        long l=1,hi=(long)1e12;
        long ans1=-1,anss2=-1;
        while (l<=hi){
            long mid=l+(hi-l)/2;
            if (cnt1<=(mid-(mid/x))){
                ans1=mid;
                hi=mid-1;
            }else l=mid+1;
        }
        l=1;hi=(long)1e12;
        while (l<=hi){
            long mid=l+(hi-l)/2;
            if (cnt2<=(mid-(mid/y))){
                anss2=mid;
                hi=mid-1;
            }else l=mid+1;
        }
        System.out.println(Math.max(ans1,anss2));
    }
    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new
                    InputStreamReader(System.in));
        }

        String next() {
            while (st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }
}