import math
import sys
sys.set_int_max_str_digits(0)
a,b,c,d = map(int,input().strip().split())
sum1 = math.floor(b/c)-math.ceil(a/c)+1
sum2 = math.floor(b/d)-math.ceil(a/d)+1
x = math.lcm(c,d)
sum3 = math.floor(b/x)-math.ceil(a/x)+1
print(b-a+1-sum1-sum2+sum3)