# https://yukicoder.me/problems/no/3775



def main():
    N, K = map(int, input().split())
    P = list(map(int,  input().split()))

    array = [[] for _ in range(K)]
    for i in range(N):
        array[i % K].append(P[i])

    answer = []
    for k in range(K):
        ar = array[k]
        for i in range(len(ar)):
            j = i
            while j > 0 and ar[j - 1] > ar[j]:
                answer.append(((j - 1) * K + k, j * K + k))
                tmp = ar[j - 1]
                ar[j - 1 ] = ar[j]
                ar[j] = tmp
                j -= 1

    ans_array = []
    for index in range(N):
        ans_array.append(array[index % K][index // K])

    for i in range(N - 1):
        if ans_array[i] > ans_array[i + 1]:
            print(-1)
            return

    print(len(answer))
    for i, j in answer:
        print(i + 1, j + 1)


        

  








if __name__ == "__main__":
    main()