# numpyチャレンジ
import numpy as np


class UnionFind:
    def __init__(self, n):
        self.par = np.array([i for i in range(n)])
        self.size = np.ones(n)

    def find(self, v):
        if v == self.par[v]:
            return v
        else:
            self.par[v] = self.find(self.par[v])
            return self.par[v]

    def unite(self, u, v):
        u = self.find(u)
        v = self.find(v)

        if u == v:
            return

        if self.size[u] < self.size[v]:
            u, v = v, u

        self.size[u] += self.size[v]
        self.par[v] = u


l, r = list(map(int, input().split()))

uf = UnionFind(r + 1)

for x in range(l, r + 1):
    y = x * 2
    while y <= r:
        uf.unite(x, y)
        y += x

ans = 0
for x in range(l, r):
    if uf.find(x) != uf.find(x + 1):
        ans += 1
        uf.unite(x, x + 1)

print(ans)