import java.io.*;
import java.util.*;

public class Main {

    public static void main(String[] args) throws IOException {
        InputStream inputStream = System.in;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(System.out);

        long a = in.nextLong(), b = in.nextLong(), c = in.nextLong(), d = in.nextLong();
        long gcd = gcd(c, d);
        long right = b - (b/c + b/d) + (b/(c * d/gcd));
        long left = a - 1 - (((a - 1) / c) + ((a - 1) / d)) + ((a - 1)/(c * d/gcd));
        out.println(right - left);
        out.close();
    }

    public static long gcd(long a, long b) {
        if (a == 0 || b == 0) return b + a;
        else return gcd(b, a % b);
    }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz