8VC Venture Cup 2017 - Elimination Round A. PolandBall and Hypothesis【水题】-优快云博客

本文链接：https://blog.youkuaiyun.com/mengxiang000000/article/details/54576311

针对波兰球提出的每个正整数n倍m加1为素数的假说，本文提供了一个程序解决方案来寻找反例，证明该假说不成立。通过简单的暴力搜索方法找到符合条件的最小m值。

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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 ≤ 10³. It is guaranteed the the answer exists.

Examples

Input

Output

Input

Output

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.

题目大意：

给你一个数字N，让你找一个解M，使得M最小，并且N*M+1不是素数。

思路：

题目中已经说明M的范围，而且很小，不妨暴力。

Ac代码：

#include<stdio.h>
#include<string.h>
#include<math.h>
using namespace std;
#define ll __int64
int judge(ll num)
{
    for(int i=2;i<=sqrt(num);i++)
    {
        if(num%i==0)return 1;
    }
    return 0;
}
int main()
{
    ll n;
    while(~scanf("%I64d",&n))
    {
        int output=0;
        for(int i=1;i<=1000;i++)
        {
            if(judge(n*i+1)==1)
            {
                printf("%d\n",i);
                break;
            }
        }
    }
}