萌新求助 为什么后三个点TLE了？

#include <bits/stdc++.h>

using namespace std;

bool prime(int n) {
    if (n <= 1) return false;
    else {
        for (int i = 2; i * i <= n; i++) {
            if (n % i == 0) return false;
        }
        return true;
    }
}

int huiwen(int num) {
    int sum = 0;
    while(num > 0) {
        sum = sum * 10 + num % 10;
        num /= 10;
    }
    return sum;
}

int main() {
    int n, m;
    cin >> n >> m;
    for (int i = n; i <= m; i++) {
        if (prime(i) && huiwen(i) == i) cout << i << endl;
    }

    return 0;
}