class UF_tree:
    def __init__(self, n):
        self.root = [-1] * (n + 1)
        self.rank = [0] * (n + 1)

    def find(self, x):
        if self.root[x] < 0:
            return x
        else:
            self.root[x] = self.find(self.root[x])
            return self.root[x]

    def isSame(self, x, y):
        return self.find(x) == self.find(y)

    def unite(self, x, y):
        x = self.find(x)
        y = self.find(y)
        if x == y:
            return
        elif self.rank[x] < self.rank[y]:
            self.root[y] += self.root[x]
            self.root[x] = y
        else:
            self.root[x] += self.root[y]
            self.root[y] = x
            if self.rank[x] == self.rank[y]:
                self.rank[x] += 1

    def size(self, x):
        return - self.root[self.find(x)]


L, R = map(int, input().split())
size = R - L + 1
uf = UF_tree(R + 1)

for i in range(L, R + 1):
    v = i * 2
    while v <= R:
        uf.unite(i, v)
        v += i

cost = 0
for i in range(L, R):
    if uf.isSame(i, i + 1):
        continue
    uf.unite(i, i + 1)
    cost += 1

print(cost)