R=range
J=lambda:list(map(int,input().split()))
O=print
N,K=J()
P=J()
S=[]
for k in R(K):
	for i in R((N-k+K-1)//K):
		for j in R(k+i*K-K,-1,-K):
			if P[j]<P[j+K]:break
			P[j],P[j+K]=P[j+K],P[j];S+=[(1+j,1+j+K)]
if all(P[i-1]<P[i]for i in R(1,N)):
	O(len(S))
	for s in S:O(*s)
else:O(-1)