class UnionFind:
    def __init__(self, n):
        self.par = [i for i in range(n+1)]
        self.rank = [0] * (n+1)

    # 検索
    def find(self, x):
        if self.par[x] == x:
            return x
        else:
            self.par[x] = self.find(self.par[x])
            return self.par[x]

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

    # 同じ集合に属するか判定
    def same_check(self, x, y):
        return self.find(x) == self.find(y)


l, r = map(int, input().split())
uf = UnionFind(r + 1)
t = [0] * (r + 1)
for i in range(l, r + 1):
    if t[i] == 0:
        for j in range(i * 2, r + 1, i):
            t[j] = 1
            uf.unite(i, j)
ans = 0
s = set()
for i in range(l, r + 1):
    p = uf.find(i)
    if p not in s:
        ans += 1
        s.add(p)
print(len(s) - 1)