def main():
    n, k = list(map(int, input().split()))
    A = list(map(lambda x: int(x)-1, input().split()))
    for i in range(n):
        if A[i] % k != i % k:
            print(-1)
            return
    Ans = []
    for u in range(n):
        for i in range(n):
            if A[i] == u:
                break
        while u < i:
            Ans.append((i-k, i))
            A[i-k], A[i] = A[i], A[i-k]
            i -= k
    print(len(Ans))
    for u, v in Ans:
        print(u+1, v+1)

main()