A. PolandBall and Hypothesis

    xiaoxiao2021-03-26  5

    time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output

    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.


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


    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.

    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.


    #include<stdio.h> #include<string.h> int main() { int n; scanf("%d",&n); if (n==1) { printf("3\n"); } else if (n==2) { printf("4\n"); } else { printf("%d\n",n-2); } return 0; }

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