N = int(input())
A = list(map(int, input().split()))

d = {}
for i, a in enumerate(A):
    if a in d:
        d[a].append(i + 1)
    else:
        d[a] = [i + 1]

l, r = 0, N
for v in d.values():
    if len(v) == 1:
        continue
    if len(v) == 2:
        l = max(l, v[0] + 1)
        r = min(r, v[1])
    else:
        exit(print(-1))

ans = list(range(l - 1, r))
print(len(ans))
print(*ans)