1
n = int(input())
2
if n % 2 != 0:
3
    print(-1)
4
else:
5
    a = []
6
    for i in range(1, n + 1, 2):
7
        a.append(i + 1)
8
        a.append(i)
9
    for x in a:
10
        print(x, end=' ')