N = int(input())
cnt = [0] * (10**5+10)
A = list(map(int,input().split()))
for i in range(N):
    cnt[A[i]] += 1

r = 10**5+4
flag = True #一度だけ
res = 0
for i in range(10**5+1):
    #print(i,cnt[:5],res)
    if cnt[i] >= 2:
        res += cnt[i] - 2
    elif cnt[i] == 0:
        print(i)
        exit()
    elif flag == False: # cnt[i] == 1:
        print(i)
        exit()
    elif flag == True: # cnt[i] == 1:
        flag = False
        if res :
            cnt[i] += 1
        else:
            while r > i:
                if cnt[r] == 0:
                    r -= 1
                else:
                    cnt[r] -= 1
                    break
            else:
                print(i)
                exit()