N = int(input())
A = [int(input()) for _ in range(N)]
B = [[] for _ in range(N)]
rem = []
tmp = N
for i in range(N):
    if A[i] < N:
        B[A[i]].append(i)
        tmp = A[i]
if tmp == N:
    for i in range(N):
        print(i)
    exit()

if len(B[tmp]) == N:
    print(-1)
    exit()

nu = []
C = []
for i in range(N):
    if B[i] == []:
        nu.append(i)
    else:
        C.append((len(B[i]),i))
C.sort()
NC = len(C)
ans = [-1] * N
if NC > 1:
    nu.append(C[-1][1])
    for _,c in C:
        for b in B[c]:
            ans[b] = nu.pop()
        nu.append(c)
elif NC == 1:
    c = C[0][1]
    ans[c] =nu.pop()
    nu.append(c)

for i in range(N):
    if ans[i] == -1:
        ans[i] = nu.pop()

for a in ans:
    print(a)