import sys

read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

class UnionFind:
    def __init__(self, N):
        self.root = list(range(N))
        self.size = [1] * (N)
        self.n_comp = N

    def find_root(self, x):
        root = self.root
        while root[x] != x:
            root[x] = root[root[x]]
            x = root[x]
        return x

    def merge(self, x, y):
        x = self.find_root(x)
        y = self.find_root(y)
        if x == y:
            return False
        sx, sy = self.size[x], self.size[y]
        if sx < sy:
            self.root[x] = y
            self.size[y] += sx
        else:
            self.root[y] = x
            self.size[x] += sy
        self.n_comp -= 1
        return True

L, R = map(int, read().split())

U = R + 10

uf = UnionFind(R + 1)

is_prime = [0] * U
is_prime[2] = 1
for p in range(3, R + 1, 2):
    is_prime[p] = 1
for p in range(3, R + 1, 2):
    if p * p > R:
        break
    for i in range(p * p, R + 1, p + p):
        is_prime[i] = 0
primes = [p for p, x in enumerate(is_prime) if x]

for p in primes:
    for i in range(L, R + 1):
        if p * i > R:
            break
        uf.merge(i, p * i)

x = uf.n_comp - L - 1
print(x)