UESTC--1272--Final Pan's prime numbers(水题)

Final Pan's prime numbers

Time Limit: 1000MS Memory Limit: 65535KB 64bit IO Format: %lld & %llu

SubmitStatus

Description

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

8

Sample Output

7

Hint

Source

第七届ACM趣味程序设计竞赛第四场（正式赛）

这一个估计就是最水的的了，找到规律之后判断一下就好

#include<string.h>#include<stdlib.h>#include<math.h>#include<iostream>#include<algorithm>using namespace std;int main(){long long n;while(scanf("%lld",&n)!=EOF){if(n<7)printf("-1\n");elseprintf("7\n");}return 0;}