import math

def prime_number(n):
	# n >= 2
	prime = []
	limit = math.sqrt(n)
	data = [i + 1 for i in range(1, n)]
	while True:
		p = data[0]
		if limit <= p:
			return prime + data
		prime.append(p)
		data = [e for e in data if e % p != 0]

l, r = map(int, input().split())
if r*(r+1) - l*(l-1) // 2 <= 1:
	p = set()
else:
	p = set(prime_number((r*(r+1) - l*(l-1)) // 2))
	
ans = 0
for i in range(l, r+1):
	tmp = 0
	for j in range(i, r+1):
		tmp += j
		if tmp in p:
			ans += 1
print(ans)