java

package com.mmanzhos;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);

        int N = in.nextInt();
        int[] ar = new int[N];


        for (int i = 0; i < N; i++) {
            ar[i] = in.nextInt();
        }

        Arrays.sort(ar);

        /*
        6
        1 3 6 1 3 5
        4

        1 1
        2

        2 2 2
        3

        3 3 3 3
        4

        4 4 4 4 4
        5

        */

        int agreed = 0;
        List<Integer> latents = new ArrayList<>();

        int lastLatent = -1;

        for (int i = 0; i < N; i++) {

            if (lastLatent != -1 && ar[lastLatent] == ar[i]) continue;


            if (ar[i] <= agreed) {
                agreed++;
            } else {
                int missing = ar[i] - agreed;
                int missingSatisfies = 0;

                for (int j = i + 1; j < N && j <= i + missing; j++) {
                    if (ar[i] == ar[j])
                        missingSatisfies++;
                }

                if (missing == missingSatisfies) {
                    agreed += missing + 1;
                    i = i + missing;
                } else {
                    latents.add(i);
                    lastLatent = i;
                }
            }
        }

        //System.out.println("Agreed now: " + agreed);


        while (!latents.isEmpty()) {
            int atLeastOneWasRemoved = 0;

            for (int i = 0; i < latents.size(); i++) {
                int index = latents.get(i);
                if (ar[index] <= agreed) {
                    agreed++;
                    latents.remove(i);
                    atLeastOneWasRemoved++;
                } else {
                    int missing = ar[index] - agreed;
                    int missingSatisfies = 0;

                    for (int j = index + 1; j < N && j <= index + missing; j++) {
                        if (ar[index] == ar[j])
                            missingSatisfies++;
                    }

                    if (missing == missingSatisfies) {
                        agreed++;
                        latents.remove(i);
                        atLeastOneWasRemoved++;
                    }
                }
            }

            if (atLeastOneWasRemoved == 0) {
                break;
            }
        }


        System.out.println(agreed);

    }

}