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

Submit
Status

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");
		else
		printf("7\n");
	}
	return 0;
}