n, k = map(int, input().split())
p = list(map(int, input().split()))
for i in range(n):
    p[i] -= 1
ans = []
for v in range(n):
    i = p.index(v)
    if i % k != v % k:
        print(-1)
        exit()
    while i != v:
        ni = i - k
        ans.append((ni, i))
        p[i], p[ni] = p[ni], p[i]
        i = ni
assert p == list(range(n))
print(len(ans))
for i, j in ans:
    print(i + 1, j + 1)