A reversible prime in any number system is a prime whose "reverse" in that number system is also a prime. For example in the decimal system 73 is a reversible prime because its reverse 37 is also a prime.

Now given any two positive integers N (<10​5​​) and D (1<D≤10), you are supposed to tell if N is a reversible prime with radix D.

Input Specification:

The input file consists of several test cases. Each case occupies a line which contains two integers N and D. The input is finished by a negative N.

Output Specification:

For each test case, print in one line Yes if N is a reversible prime with radix D, or No if not.

Sample Input:

73 10
23 2
23 10
-2

Sample Output:

Yes
Yes
No

 程式碼如下：

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <iostream>
#include <math.h>
#include <vector>
using namespace std;
int n,d;
vector<int>ans;
bool is_prime(int x)
{
    if(x==0||x==1)
        return false;
    for (int i=2;i<=sqrt(x);i++)
    {
        if(x%i==0)
        {
            return false;
        }
    }
    return true;
}
int main()
{
    while(scanf("%d",&n))
    {
        ans.clear();
        if(n<0)
        {
            break;
        }
        scanf("%d",&d);
        if(is_prime(n)==false)
        {
            printf("No\n");
            continue;
        }
        while (n)
        {
            ans.push_back(n%d);
            n/=d;
        }
        int sum=0;
        for (int i=ans.size()-1,j=1;i>=0;i--,j*=d)
        {
            sum+=ans[i]*j;
        }
        if(is_prime(sum))
        {
            printf("Yes\n");
        }
        else
        {
            printf("No\n");
        }
    }
    return 0;
}