from collections import Counter

n = int(input())
A = list(map(int, input().split()))
counter = Counter(A)

add = 0
for i in range(10**5 + 1):
    if counter[i] >= 2:
        if counter[i] >= 3:
            add = 1
        continue
    if counter[i] == 1:
        if add == 0:
            for j in range(i + 1, 10**5 + 1):
                if counter[j] > 0:
                    add = 1
                    break
        print(i + add)
        break
    print(i)
    break