n,k,*p=map(int,open(0).read().split())
q=p[:]
for i in range(k):
  q[i:n:k]=sorted(p[i:n:k])
if q!=sorted(p):
  exit(print(-1))
ans=[]
for i in range(k):
  for j in range(i,n,k):
    # print(i,j,q[j],p[j])
    if q[j]!=p[j]:
      r=p.index(q[j])
      for _ in range((r-j)//k):
        ans+=(r-k,r),
        p[r-k],p[r]=p[r],p[r-k]
        r-=k
        # print(i,j,q[j],p)
assert p==sorted(p)
print(len(ans))
for i,j in ans:
  print(i+1,j+1)