human
I found an interesting problem on https://codeforces.com/problemset/problem/755/A:
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.

-----Input-----

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

-----Output-----

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 ≤ 10^3. It is guaranteed the the answer exists.

-----Examples-----
Input
3

Output
1
Input
4

Output
2

-----Note-----

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.

I tried it in Python, but could not do it. Can you solve it?
assistant
#Here is the Python program you requested.

def primesSieve(limit):
    def internalPrimesSieve(limit):
        a = [True] * limit # Initialize the primality list
        a[0] = a[1] = False

        for (i, isprime) in enumerate(a):
            if isprime:
                yield i
                for n in range(i*i, limit, i): # Mark factors non-prime
                    a[n] = False
    return [p for p in internalPrimesSieve(limit)]

n = int(input())
primes = primesSieve(1000002)
for i in range(1,1001):
    if n*i + 1 not in primes:
        print(i)
        break