# https://github.com/robe2222555/atcoder-lib/blob/main/template/python/main.py
import sys
input = lambda: sys.stdin.readline().rstrip()
def LI(): return list(map(int, input().split()))
def II(): return int(input())


INF = 1<<60
def solve():
	N,K = LI()
	A = LI()
	for i in range(N): A[i]-=1
	ans = []
	for i in range(N):
		if A[i]!=i:
			for j in range(N)[::-1]:
				if A[j] == i:
					if (j-i)%K != 0:
						print(-1)
						return
					while j>i:
						nx = j-K
						A[nx],A[j] = A[j],A[nx]
						ans.append((nx+1, j+1))
						j = nx
						continue
					break
	print(len(ans))
	for a in ans: print(*a)
	return


def main():
	T = 1
	for _ in range(T):
		solve()
	return


if __name__ == '__main__':
	main()