Description

A palindromic prime is simultaneous a prime number and palindromic.

For example, 131 is a prime and also a palindromic.

Write a program that reads an interger n, and finds the nth palindromic prime.

Input

An interger n (1<=n<=50).

Output

The nth palindromic prime.

Sample Input

7

Sample Output

131

//   Date:2020/4/9
//   Author:xiezhg5
#include <stdio.h>
int isPrime(long n);
long reverse(long n);
long isPalindrome(long n);
int main(void)
{
    int num, i, cnt = 0;
    while (1) 
	{
        scanf("%d",&num);                    //输入第几个回文素数 
        if ((num>=1) && (num<=50) ) break;   //读入一个标准数立即判断 
    }
    i = 2;
    while (1) 
	{
    	//调用isPrime和 isPalindrome函数 
        if ( isPrime(i) && isPalindrome(i)) cnt ++;   //启用累加器 
        if (cnt == num) break;
        i ++;
    }
    printf("%d",i);
    return 0;
}
//判断n是不是素数 
int isPrime(long n) 
{
    int i;
    if (n == 2)
        return 1;
    for (i = 2; i*i <= n;i++)
        if (n % i == 0)
             return 0;
     return 1;    
}
//返回逆序后的n 
long reverse(long n) 
{
	int reverseNumber = 0;
	//求各进制位上的数字 
	do 
	{
	    reverseNumber = reverseNumber * 10 + n % 10;
		n /= 10;
	}while(n > 0);
	return reverseNumber;
}
//反转后的n与原来的n对比判断是否回文数 
long isPalindrome(long n) 
{
	return reverse(n) == n;
}