n,k = map(int, input().split())
p = list(map(int, input().split()))
ans = []
for i in range(1,n+1):
  now = p.index(i)
  while now != i-1:
    if now-k < i-1:
      print(-1)
      exit()
    p[now],p[now-k] = p[now-k],p[now]
    ans.append([now-k+1,now+1])
    now -= k

print(len(ans))
for i in ans:
  print(*i)