PAT乙级1059C语言竞赛（20分）运行超时，求大佬解答

请问一下各位大佬，我做PAT乙级“1059C语言竞赛（20分）”那道题的时候，代码如下，实在搞不懂为什么测试点1和2会运行超时，请大佬指点，小菜鸟感激不尽????

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <math.h>
using namespace std;

bool isPrime(int c) {
    for (int i = 2; i <= sqrt(c); i++) {
        if (c % i == 0) return false;
    }
    return true;
}

int main() {
    int N; cin >> N;
    vector<string> vec(N), checked;
    for (int i = 0; i < N; i++) cin >> vec[i];
    int m; cin >> m;
    string c;
    int rank;
    for (int i = 0; i < m; i++) {
        cin >> c;
        if (find(checked.begin(), checked.end(), c) != checked.end()) { cout << c << ": Checked" << endl; continue; }
        rank = find(vec.begin(), vec.end(), c) - vec.begin();
        if (rank == N) cout << c << ": Are you kidding?" << endl;
        else if (rank == 0) { cout << c << ": Mystery Award" << endl; checked.push_back(c); }
        else if (isPrime(rank+1)) { cout << c << ": Minion" << endl; checked.push_back(c); }
        else { cout << c << ": Chocolate" << endl; checked.push_back(c); }
    }
    return 0;
}