import sys

data = sys.stdin.readline().split(" ")
n = int(data[0])

l = []
for i in range(1, len(data)):
    l.append(int(data[i]))

l.sort()

min=l[0]
max=l[-1]

if min==1:
    print(0)
else:
    for i in range(min,max+1):

        if i not in l:
            print(i)