import java.util.*;

class Solution {
    public int solution(int[] citations) {
        List<Integer> answerList = new ArrayList<>();

        Arrays.sort(citations);

        for (int i = 0; i < citations.length; i++) {
            if (citations[i] >= citations.length - i) {
                answerList.add(citations.length - i);
            }
        }
        return answerList.isEmpty() ? 0 : answerList.get(0);
    }
}