import sys
input = sys.stdin.readline

N,K=list(map(int,input().split()))
A=list(map(int,input().split()))

ANS=[]

for i in range(1,N+1):
    x=A.index(i)

    if x%K!=(i-1)%K:
        print(-1)
        exit()

    for j in range(x,i-1,-K):
        ANS.append((j-K,j))
        A[j-K],A[j]=A[j],A[j-K]

#print(A)

print(len(ANS))

for x,y in ANS:
    print(x+1,y+1)