UESTC 1272-Final Pan's prime numbers

Final Pan's prime numbers

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Time Limit: 3000/1000MS (Java/Others)     Memory Limit: 65535/65535KB (Java/Others)

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Final Pan likes prime numbers very much.

One day, he want to find the super prime numbers.A prime numbers n (n >4) is a super prime number only if n -4 and n +4 are both prime numbers,too.

Your task is really easy：Give N ，find the maximum super prime number n  that n <=N .

Input

Only one integer N.(4<N<10 12 ) 

Output

If there is no such interger n ，print'−1 ',otherwise print n .

Sample input and output

Sample InputSample Output

8

7

Hint

Source

第七届ACM趣味程序设计竞赛第四场（正式赛） 

题目大意：

题意就是找到1-n区间里面最大的素数，并且i+4和i-4都是素数。

解题思路：

很简单，你会发现只有7符合这个条件。

#include<stdio.h>#include<string.h>#include<algorithm>int main(){int nn;while(scanf("%d",&nn)!=EOF){if(nn>6)printf("7\n");elseprintf("-1\n");}return 0;}