# AtCoder Competition Template v2.3.2 SHORT (PyPy 7.3.20 / Python 3.11)
# ↑ https://github.com/Rino-program/atcoder/blob/main/.template/main.py &template.py
# ALL: https://github.com/Rino-program/atcoder/blob/main/.template/template.py

import os, sys
from collections import deque, defaultdict, Counter
from itertools import permutations, combinations, accumulate, product, chain
#from sortedcontainers import SortedSet, SortedList, SortedDict
from bisect import bisect_left, bisect_right
from copy import deepcopy
import operator
import heapq
import math
import string

# ===== 設定・制限解除 =====
#sys.setrecursionlimit(2*10**6)

# ===== 入力ヘルパ =====
input = lambda: sys.stdin.readline().rstrip()
INT = lambda: int(input())
INT0 = lambda: int(input()) - 1
MAP = lambda: map(int, input().split())
MAP0 = lambda: (int(x) - 1 for x in input().split())
LIST = lambda: list(map(int, input().split()))
LIST0 = lambda: [int(x) - 1 for x in input().split()]
TUPLE = lambda: tuple(map(int, input().split()))
TUPLE0 = lambda: tuple(int(x) - 1 for x in input().split())
LISTS = lambda n: [list(map(int, input().split())) for _ in range(n)]
LISTS0 = lambda n: [[int(x) - 1 for x in input().split()] for _ in range(n)]
TUPLES = lambda n: [tuple(map(int, input().split())) for _ in range(n)]
TUPLES0 = lambda n: [tuple(int(x) - 1 for x in input().split()) for _ in range(n)]
LISTSI = lambda n: [int(input()) for _ in range(n)]
LISTSI0 = lambda n: [int(input()) - 1 for _ in range(n)]
STR = lambda: input()
STRS = lambda n: [input() for _ in range(n)]
CHARS = lambda: list(input())
CHARSL = lambda n: [list(input()) for _ in range(n)]
CHARSLI = lambda n: [list(map(int, input())) for _ in range(n)]

# ===== 高速 print =====
def print(*args, sep=' ', end='\n', file=None, flush=False):
    file = file or sys.stdout
    sep = ' ' if sep is None else sep
    end = '\n' if end is None else end
    file.write(sep.join(map(str, args)) + end)
    flush and file.flush()

# ===== 定数 =====
INF = 10 ** 18
MOD = 998244353
# MOD = 10**9 + 7

# ===== 関数短縮 =====
pr = print
en = enumerate
hepu = heapq.heappush
hepo = heapq.heappop
bil = bisect_left
bir = bisect_right
dedict = defaultdict

# ===== 方向ベクトル(上(負)から時計回り) =====
DIR4 = ((-1, 0), (0, 1), (1, 0), (0, -1))
DIR8 = ((-1, 0), (-1, 1), (0, 1), (1, 1), (1, 0), (1, -1), (0, -1), (-1, -1))
DIR9 = DIR8 + ((0, 0),) # 中央は最後

# ===== 文字列のリスト =====
LOWER = list(string.ascii_lowercase) # 小文字 a-z の文字列リスト
UPPER = list(string.ascii_uppercase) # 大文字 A-Z の文字列リスト
DIGITS = list(string.digits) # 数字 0-9 の文字列リスト

# ===== よく使う出力関数 =====
Yes = lambda **kwargs: print("Yes", **kwargs)
No = lambda **kwargs: print("No", **kwargs)
yes = lambda **kwargs: print("yes", **kwargs)
no = lambda **kwargs: print("no", **kwargs)
YES = lambda **kwargs: print("YES", **kwargs)
NO = lambda **kwargs: print("NO", **kwargs)

def yn(cond: bool, yes: str = "Yes", no: str = "No", **kwargs) -> None:
    """条件に応じてYes/No出力"""
    print(yes if cond else no, **kwargs)

def print_grid(grid: list[list], sep: str = '') -> None:
    """グリッド表示"""
    print('\n'.join(sep.join(map(str, row)) for row in grid))

# ===== デバッグ =====
# AtCoder提出時は自動で無力化
if "ATCODER" not in os.environ and "ONLINE_JUDGE" not in os.environ:
    def debug(*args, sep=' ', end='\n', flush=False) -> None:
        """デバッグ出力（標準エラー）"""
        print("[DEBUG]", *args, sep=sep, end=end, file=sys.stderr, flush=flush)
else:
    def debug(*args, **kwargs) -> None:
        pass

# ===== template.py より引用コード =====

# ==============================================
# =================== main =====================
# ==============================================

def main() -> None:
    # ここに解答を書く
    N, K = MAP()
    P = LIST()
    d = dedict(int)
    for i, p in en(P):
        d[p] = i
    ans = []
    for i in range(N, 0, -1):
        if P[i-1] != i:
            if abs(d[i] - (i-1)) % K != 0:
                print(-1)
                return
            for j in range(abs(d[i] - (i-1)) // K):
                #debug(i, j)
                #debug(d)
                #debug(P)
                #debug(P[d[i]], P[d[i]+K])
                ans.append(f"{d[i]+1} {d[i]+K+1}")
                pos = d[i]
                other = pos + K
                a, b = P[pos], P[other]
                d[a], d[b] = other, pos
                P[pos], P[other] = b, a
                #debug(d)
                #debug(P)
    print(len(ans))
    print(*ans, sep="\n")
















if __name__ == "__main__":
    main()