def mex(S):
    x=0
    while x in S:
        x+=1
    return x

def solve():
    from collections import Counter

    N=int(input())
    A=list(map(int,input().split()))

    A_max=max(A)
    C=[0]*(max(A)+2)
    for a in A:
        C[a]+=1

    for a in range(A_max+2):
        if C[a]==0:
            return a
        elif C[a]==1:
            for b in range(a+1,A_max+1):
                if C[b]:
                    return a+1
            else:
                return a

#==================================================
print(solve())