n, k = map(int, input().split())
p = list(map(int, input().split()))

swap = []
for d in range(k):
    arr = list(range(d, n, k))
    for i in arr:
        for j in arr[::-1]:
            if i >= j: continue
            if p[j - k] > p[j]:
                p[j - k], p[j] = p[j], p[j - k]
                swap.append((j - k, j))

is_sorted = True
for i in range(n - 1):
    is_sorted &= p[i] <= p[i + 1]

if is_sorted:
    print(len(swap))
    for i, j in swap:
        print(i + 1, j + 1)
else:
    print(-1)