UESTC Final Pan's prime numbers 1272 （坑）

Final Pan's prime numbers

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<1012)

Output

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

Sample input and output

Source

#include<stdio.h>
#include<string.h>
#include<math.h>
#include<algorithm>
#define ll long long
using namespace std;
int main()
{
	int n;
	while(scanf("%d",&n)!=EOF)
	{
		if(n==5||n==6)
			printf("-1\n");
		else
			printf("7\n");
	}
	return 0;
}