def prime_counting(n):
    if n <= 1: return 0
    r = int(n**0.5)
    assert r*r <= n < (r+1)**2
    V = [0] + [n//i for i in range(1,r+1)] + list(range(n//r-1,0,-1))
    S = [i-1 for i in V]
    for p in range(2,r+1):
        if S[-p] > S[-p+1]:  # p is prime
            sp = S[-p+1]  # number of primes smaller than p
            p2 = p*p
            for i in range(1,2*r+1):
                v = V[i]
                if v < p2: break
                S[i] -= (S[-(v//p) if v//p <= r else i*p] - sp)
    return S[1]

L,R = map(int,input().split())
ans = prime_counting(R) - prime_counting(L-1)
if L < R: ans += prime_counting(2*R-1) - prime_counting(2*L)
print(ans)