import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.InputMismatchException;
import java.util.Scanner;

/**
 * Created by hp on 7/29/2017.
 */
public class toto {
    static long []fib=new long[80];
    static StringBuilder fib_s ;
    static boolean []valid=new boolean[700];
    public static void main(String[] args) {

        InputReader in=new InputReader(System.in);
        PrintWriter out=new PrintWriter(System.out);
        long cnt1=in.nextLong();
        long cnt2=in.nextLong();
        long x=in.nextLong();
        long y=in.nextLong();
        long l=1;
        long r=999999999;
        while (r-l>1)
        {
            long m=(l+r)>>1;
            if(bs(cnt1,cnt2,x,y,m))
            {
              // out.println("true");
                r=m;
            }else
            {
               // out.println("false");
                l=m;
            }
        }
        out.print(r);
        out.close();


    }
    public static boolean bs(long cnt1,long cnt2,long x,long y,long mid)
    {
        long cntxy = mid/ (x * y);
        long cntx = mid / x - cntxy;
        long cnty = mid/ y - cntxy;
        long common = mid - cntx - cnty - cntxy;

        if (common + cnty < cnt1)
            return false;
        common -= Math.max(0, cnt1 - cnty);
        return common + cntx >= cnt2;

    }
    static class InputReader {

        private InputStream stream;
        private byte[] buf = new byte[8192];
        private int curChar, snumChars;
        private InputReader.SpaceCharFilter filter;

        public InputReader(InputStream stream) {
            this.stream = stream;
        }

        public int snext() {
            if (snumChars == -1)
                throw new InputMismatchException();
            if (curChar >= snumChars) {
                curChar = 0;
                try {
                    snumChars = stream.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }
                if (snumChars <= 0)
                    return -1;
            }
            return buf[curChar++];
        }

        public int nextInt() {
            int c = snext();
            while (isSpaceChar(c))
                c = snext();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = snext();
            }
            int res = 0;
            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = snext();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public long nextLong() {
            int c = snext();
            while (isSpaceChar(c))
                c = snext();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = snext();
            }
            long res = 0;
            do {
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = snext();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public int[] nextIntArray(int n) {
            int a[] = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public String readString() {
            int c = snext();
            while (isSpaceChar(c))
                c = snext();
            StringBuilder res = new StringBuilder();
            do {
                res.appendCodePoint(c);
                c = snext();
            } while (!isSpaceChar(c));
            return res.toString();
        }

        public boolean isSpaceChar(int c) {
            if (filter != null)
                return filter.isSpaceChar(c);
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);
        }
    }

}
