Please help me debug my code for CRFTEST

I have a question for CFRTEST. I keep getting a WA. Here's my code:

#include <iostream>
#include <algorithm>
#include <cmath>

using namespace std;

int main() {

    int cases;
    cin >> cases;

    for (int case_no = 0; case_no < cases; case_no++) {

        int friends;
        cin >> friends;

        int deadlines[friends];

        for (int i = 0; i < friends; i++) {
            cin >> deadlines[i];
        }

        sort(deadlines, deadlines + friends);

        int count = 0;
        int filled_till = 0;

        for (int i = 0; i < friends; i++) {
            if (deadlines[i] > filled_till) {
                filled_till++;
                count++;
            }
        }

        cout << count << endl;

    }

    return 0;

}

Could anybody please help me recognize the flaw? It works well on all the testcases I've tried.