L,R = map(int, input().split())
count = 0

def eratosthenes_sieve(n):
    is_prime = [True]*(n + 1)
    is_prime[0] = is_prime[1] = False
    for p in range(2, n + 1):
        if is_prime[p]:
            for q in range(2*p, n + 1, p):
                is_prime[q] = False
    return is_prime

n = 10**6
is_prime = eratosthenes_sieve(n)
for i in range(L-1,R):
    for j in range(i,R):
        s = i+1
        for k in range(i+1,j+1):
            s += (k+1)
        if is_prime[s] == True:
            count += 1

print(count)