230228 [1327: 소트게임]

import sys
from collections import deque

input = sys.stdin.readline

N, K = map(int, input().rstrip().split())
P = list(input().rstrip().split())

visited = set("".join(P))
q = deque([["".join(P),0]])

ans = -1

while(q):
    word, cnt = q.popleft() # 단어, 단어를 바꾼 횟수
    tmpP = list(word)
    
    if tmpP == sorted(tmpP):
        ans = cnt
        break

    isFrist = False
    
    for i in range(N-K+1):
        newP = list(tmpP)
        targetP = newP[i:i+K]
        targetP.reverse()
        for j in range(K):
            newP[i+j]=targetP[j]
        newWord = "".join(newP)
        if newWord not in visited:
            visited.add(newWord)
            q.append([newWord, cnt+1])

print(ans)