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();
        double n= (double) cnt1/(x-1);
        double m= (double) cnt2/(y-1);
        int ans=(int) Math.ceil(Math.max(n*x-1,m*y-1));
//        System.out.println(m+" "+y);
        System.out.println(ans);

    }
    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;
        }
    }
}