N = int(input())
L = []
while True:
try:
L.extend(list(input().split()))
except:
break
numbers = []
for s in range(N):
for e in range(s+1, N+1):
numbers.append(int("".join(L[s:e])))
numbers = list(set(numbers))
numbers.sort()
mn = -1
for i in numbers:
if i == mn + 1:
mn+=1
elif i > mn + 1:
print(mn + 1)
break