n, m = map(int, input().split())

dat = [int(input()) for _ in range(m)]

sdat = set(dat)
missing = [x for x in range(1, n + 1) if x not in sdat]

res = []
i = 0
j = 0
while i < len(dat) and j < len(missing):
    if dat[i] < missing[j]:
        res.append(dat[i])
        i += 1
    else:
        res.append(missing[j])
        j += 1
while i < len(dat):
    res.append(dat[i])
    i += 1
while j < len(missing):
    res.append(missing[j])
    j += 1

for x in res:
    print(x)