import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long a = sc.nextLong();
        long b = sc.nextLong();
        long c = sc.nextLong();
        long d = sc.nextLong();
        long g = gcd(c,d);
        long q = c * d / g;
        long r = b - a - (((b / c - (a - 1) / c) + b / d - (a - 1) / d) - b / q + (a - 1) / q) + 1;
        System.out.println(r);
    }
    public static long gcd(long a,long b) {
        if(a % b == 0) {
            return b;
        }
        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