import sys
import math
#from collections import deque, defaultdict, Counter
#import heapq
#import bisect
#import itertools
#import functools

# 外部ライブラリ（AtCoder環境で利用可能）
#from sortedcontainers import SortedList, SortedSet, SortedDict
#from atcoder.dsu import DSU
#from atcoder.segtree import SegTree
#from atcoder.lazysegtree import LazySegTree
#from atcoder.fenwicktree import FenwickTree

# 入力高速化
#input = sys.stdin.readline
# 再帰回数上限
sys.setrecursionlimit(10**9)

# よくあるmod
#MOD = 1000000007
MOD = 998244353

def solve():
    # 解答ここから
    import heapq
    N, K = map(int, input().split(' '))
    A = list(map(int, input().split(' ')))
    sp = [[] for _ in range(K)]
    for i in range(N):
        sp[i % K].append(A[i])

    answer = []

    for k in range(K):
        L = len(sp[k])
        S = list(sorted(sp[k]))
        for i in range(L): # 目標位置
            j = sp[k].index(S[i])
            for l in range(i, j):
                answer.append((K*l + k, K*(l+1) + k))
                sp[k][l], sp[k][l+1] = sp[k][l+1], sp[k][l]
    res = [0] * N
    for k in range(K):
        L = len(sp[k])
        for i in range(L):
            res[K*i+k] = sp[k][i]
    if res != list(range(1, N+1)):
        print(-1)
        return
    print(len(answer))
    for f, t in answer:
        print(f+1,t+1)
if __name__ == '__main__':
    T = 1
    for _ in range(T):
        solve()