UESTC 1272 Final Pan's prime numbers(乱搞)

题目链接

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

题解：暴力超时，遂乱搞，这种题可以自己跑个1000组下来，最后发现满足这个条件的数只有一个7...

#include <cstdio>
#include <iostream>
#include <string>
#include <sstream>
#include <cstring>
#include <stack>
#include <queue>
#include <algorithm>
#include <cmath>
#include <map>
#define PI 3.1415926
#define ms(a) memset(a,0,sizeof(a))
#define msp memset(mp,0,sizeof(mp))
#define msv memset(vis,0,sizeof(vis))
using namespace std;
//#define LOCAL
bool prime(int n)
{
    if(n==2)return true;
    for(int i=2;i<=sqrt(n);i++)
    {
        if(n%i==0)return false;
    }
    return true;
}
int main()
{
#ifdef LOCAL
    freopen("in.txt", "r", stdin);
#endif // LOCAL
    //Start
    long long n;
    while(cin>>n)
    {
        if(n>=7)printf("7\n");
        else printf("-1\n");
    }
    return 0;
}