哪里错了，求调

#include<iostream>
#include<cstdio>
#include<cmath>
#include<string>
using namespace std;
bool isPrime(int x)
{
	if (x == 1)
	{
		return false;
	}
	if (x == 2 || x == 3)
	{
		return true;
	}
	for (int i = 2; i <= sqrt(x); i++)
	{
		if (x % i == 0)
		{
			return false;
		}
	}
	return true;
}
int main()
{
	int n;
	cin >> n;
	int ans = 0;
	for (int i = 11; i <= n; i++)
	{
		string s;
		s = to_string(i);
		int len = s.length();
		for (int j = 0; j < len/2; j++)
		{
			if (s[j] == s[len - 1 - j]&& isPrime(i))
			{
				ans++;
			}
		}
	}
	cout << ans;
	return 0;
}