import java.util.*;
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 ans = (B / C - (A - 1) / C) + (B / D - (A - 1) / D) - (B / lcm(C, D) - (A - 1) / lcm(C, D));
		System.out.println(B - A - ans + 1);
	}
	
	static long lcm(long m, long n) {
	    return m * n / gcd(m, n);
	}

	static long gcd (long a, long b) {
		return b > 0 ? gcd(b, a % b) : a;
	}
}

/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