CF80A.Panoramix's Prediction

A prime number is a number which has exactly two distinct divisors: one and itself. For example, numbers 2, 7, 3 are prime, and 1, 6, 4 are not.

The next prime number after x is the smallest prime number greater than x. For example, the next prime number after 2 is 3, and the next prime number after 3 is 5. Note that there is exactly one next prime number after each number. So 5 is not the next prime number for 2.

One cold April morning Panoramix predicted that soon Kakofonix will break free from his straitjacket, and this will be a black day for the residents of the Gallic countryside.

Panoramix's prophecy tells that if some day Asterix and Obelix beat exactly x Roman soldiers, where x is a prime number, and next day they beat exactly y Roman soldiers, where y is the next prime number after x, then it's time to wait for Armageddon, for nothing can shut Kakofonix up while he sings his infernal song.

Yesterday the Gauls beat n Roman soldiers and it turned out that the number n was prime! Today their victims were a troop of m Romans (m > n). Determine whether the Gauls should wait for the black day after today's victory of Asterix and Obelix?

质数是指恰好有两个不同正因数的数：1 和它本身。例如，2、7、3 是质数，而 1、6、4 不是质数。

大于 $x$ 的下一个质数，是指严格大于 $x$ 的最小质数。例如，2 之后的下一个质数是 3，3 之后的下一个质数是 5。注意：对任意整数 $x$，其“下一个质数”是唯一确定的。因此，5 并不是 2 的下一个质数。

一个寒冷的四月清晨，帕诺拉米克斯预言：卡科冯克斯很快将挣脱他的紧身衣，这将是高卢乡村居民的“黑色之日”。

帕诺拉米克斯的预言指出：若某一天阿斯特里克斯和奥贝利克斯恰好击败了 $x$ 名罗马士兵（其中 $x$ 是质数），而第二天他们又恰好击败了 $y$ 名罗马士兵（其中 $y$ 是 $x$ 之后的下一个质数），那么“末日之战”（Armageddon）即将来临——因为届时再没有任何东西能阻止卡科冯克斯放声高唱他那地狱般的歌曲。

昨天，高卢人击败了 $n$ 名罗马士兵，且已知 $n$ 是一个质数！今天，他们的对手是一支由 $m$ 名罗马士兵组成的队伍（满足 $m > n$）。请判断：在阿斯特里克斯和奥贝利克斯取得今日胜利后，高卢人是否应当为“黑色之日”做好准备？

The first and only input line contains two positive integers — n and m (2 ≤ n < m ≤ 50). It is guaranteed that n is prime.

Pretests contain all the cases with restrictions 2 ≤ n < m ≤ 4.

第一行且唯一一行输入包含两个正整数 $n$ 和 $m$（$2 \le n < m \le 50$）。保证 $n$ 是质数。

预测试包含了所有满足限制条件 $2 \le n < m \le 4$ 的情况。

Print YES, if m is the next prime number after n, or NO otherwise.

如果 $m$ 是 $n$ 之后的下一个质数，则输出 YES，否则输出 NO。