CF755A.PolandBall and Hypothesis

PolandBall is a young, clever Ball. He is interested in prime numbers. He has stated a following hypothesis: "There exists such a positive integer n that for each positive integer m number n·m + 1 is a prime number".

Unfortunately, PolandBall is not experienced yet and doesn't know that his hypothesis is incorrect. Could you prove it wrong? Write a program that finds a counterexample for any n.

PolandBall 是一个年轻而聪明的小球，他对质数很感兴趣。他提出了如下假设：“存在某个正整数 $n$，使得对任意正整数 $m$，数 $n \cdot m + 1$ 均为质数”。

不幸的是，PolandBall 的经验尚浅，尚未意识到该假设是错误的。你能证明它不成立吗？请编写一个程序，对任意给定的 $n$，找出一个反例。

The only number in the input is n (1 ≤ n ≤ 1000) — number from the PolandBall's hypothesis.

输入中唯一的数字是 $n$（$1 \leq n \leq 1000$）——即 PolandBall 假设中的那个数。

Output such m that n·m + 1 is not a prime number. Your answer will be considered correct if you output any suitable m such that 1 ≤ m ≤ 103. It is guaranteed the the answer exists.

输出一个满足 $n \cdot m + 1$ 不是质数的 $m$。只要输出任意一个满足 $1 \leq m \leq 10^3$ 的合适 $m$，你的答案即被视为正确。题目保证这样的 $m$ 一定存在。

A prime number (or a prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself.

For the first sample testcase, 3·1 + 1 = 4. We can output 1.

In the second sample testcase, 4·1 + 1 = 5. We cannot output 1 because 5 is prime. However, m = 2 is okay since 4·2 + 1 = 9, which is not a prime number.

质数（或素数）是指大于 1 的自然数，且除了 1 和它本身之外没有其他正因数。

对于第一个样例测试用例，$3\cdot1+1=4$，因此我们可以输出 $1$。

对于第二个样例测试用例，$4\cdot1+1=5$。我们不能输出 $1$，因为 $5$ 是质数。然而，$m=2$ 是可行的，因为 $4\cdot2+1=9$，而 $9$ 不是质数。