Sexy prime number (summer vacation daily question 1)

“ Sexy prime ” It is shaped like $(p,p+6)$ Such a pair of prime numbers .

It's called , Because the Latin tube “ 6、 ... and ” It's called “$sex$”（ That is, English “ sexy ”）.

Now give an integer , Please judge whether it is a sexy prime .

Input format
Input gives a positive integer on a line $N$.

Output format
if $N$ It's a sexy prime , Output in one line Yes, And output and on the second line $N$ Another sexy prime paired （ If such a number is not unique , The one with the smaller output ）.

if $N$ Not a sexy prime , Output in one line No, Then output greater than... On the second line $N$ The minimum number of sexy prime .

Data range
$1\le N\le 10^8$

sample input 1：

47

sample output 1：

Yes
41

sample input 2：

21

sample output 2：

No
23

---

#include<iostream>

using namespace std;

bool is_prime(int n){
    
    if(n < 2) return false;
    
    for(int i = 2; i <= n / i; i++)
        if(n % i == 0) return false;
        
    return true;
}

int is_sex_prime(int x){
    
    
    if(is_prime(x) && is_prime(x - 6)) return -1;
    if(is_prime(x) && is_prime(x + 6)) return 1;
    
    return 0;
}

int main(){
    
    
    int n;
    cin >> n;
    int flag = is_sex_prime(n);
    if(!flag) {
    
        puts("No");
        while(!is_sex_prime(n)) n++;
        cout << n << endl;
        
    }else{
    
        puts("Yes");
        if(flag == -1) cout << n - 6 << endl;
        else cout << n + 6 << endl;
    }
    
    return 0;
}