import java.util.*;
public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		// 整数の入力
		long A = sc.nextLong();
      long B = sc.nextLong();
      long C = sc.nextLong();
      long D = sc.nextLong();
      long bmade = B/C+B/D-B/(lcm(C,D));
      long amade = (A-1)/C+(A-1)/D-(A-1)/(lcm(C,D));
      

 
      System.out.println(B-A-(bmade-amade)+1);
    }
  
  private static long lcm(long m, long n) {
    return m * n / gcd(m, n);
}
  
  private static long gcd(long m, long n) {
    if(m < n) return gcd(n, m);
    if(n == 0) return m;
    return gcd(n, m % n);
}
}
/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