#
# 二部グラフの最大マッチング
#

import sys
sys.setrecursionlimit(10 ** 6)

def max_bipartite_matching(g):
    def rec(p, left, right, used) -> bool:
        for i in range(len(right)):
            if g[p][i] and right[i] == -1:
                left[p] = i
                right[i] = p
                return True
        for i in range(len(right)):
            if g[p][i] and not used[i]:
                used[i] = True
                if rec(right[i], left, right, used):
                    left[p] = i
                    right[i] = p
                    return True
        return False

    left = [-1] * len(g)
    right = [-1] * len(g[0])
    cnt = 0
    for i in range(len(left)):
        used = [False] * len(left)
        if rec(i, left, right, used):
            cnt += 1
    return cnt, left, right


N = int(input())
a = [int(input()) for _ in range(N)]

g = []
for i in range(N):
    g.append([True] * N)
    if a[i] < N:
        g[i][a[i]] = False

cnt, left, right = max_bipartite_matching(g)
if cnt == len(left):
    for e in left:
        print(e)
else:
    print(-1)