# your code goes here
n = int(input())
nums = list(map(int, input().split()))
def findClosestRefuge(nums):
nums.sort()
n = 1
l = len(nums)
for i in range(1, l):
if nums[i] != nums[i-1]:
nums[n] = nums[i]
n += 1
for i in range(len(nums)):
if nums[i] != i+1:
print(i+1)
break
findClosestRefuge(nums)
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