<p>Given an integer n, return <em>the smallest <strong>prime palindrome</strong> greater than or equal to </em><code>n</code>.</p>

<p>An integer is <strong>prime</strong> if it has exactly two divisors: <code>1</code> and itself. Note that <code>1</code> is not a prime number.</p>

<ul>
	<li>For example, <code>2</code>, <code>3</code>, <code>5</code>, <code>7</code>, <code>11</code>, and <code>13</code> are all primes.</li>
</ul>

<p>An integer is a <strong>palindrome</strong> if it reads the same from left to right as it does from right to left.</p>

<ul>
	<li>For example, <code>101</code> and <code>12321</code> are palindromes.</li>
</ul>

<p>The test cases are generated so that the answer always exists and is in the range <code>[2, 2 * 10<sup>8</sup>]</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> n = 6
<strong>Output:</strong> 7
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> n = 8
<strong>Output:</strong> 11
</pre><p><strong class="example">Example 3:</strong></p>
<pre><strong>Input:</strong> n = 13
<strong>Output:</strong> 101
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= n &lt;= 10<sup>8</sup></code></li>
</ul>

class Solution {
public:
    int primePalindrome(int n) {
        /*
            all even length palindrome number = 11*k

            10, 101
            11, 111
            12, 121
            20, 202
        */
        if(n>=8 && n<=11) return 11;
        int digit = to_string(n).size();
        int half = digit/2;
        for(int x=pow(10, half-1); x<1000000; x++){
            string s = to_string(x);
            string reverse_s(s.rbegin(), s.rend());
            int num = stoi(s + reverse_s.substr(1));
            if(num>=n && isPrime(num)) return num;
        }
        return -1;
    }

    bool isPrime(int num){
        if(num<2 || num%2==0) return num==2;
        for(int i=3; i*i<=num; i+=2) if(num%i==0) return false;
        return true;
    }
};
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