# your code goes here



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

li = list(map(int,input().split()))	

if N == K:

	print((1))

	quit()

i = 1

N = N-K



while N >= K:

	N = N - K +1

	i = i + 1



print((i+1))
import sys

input = sys.stdin.readline



n,k = list(map(int,input().split()))

a = list(map(int,input().split()))



res = 1

cnt = k



if n <= cnt:

    print(res)

else:

    if (n-k)%(k-1) == 0:

        print((1 + (n-k)//(k-1)))

    else:

        print((1 + (n-k)//(k-1)+1))
# your code goes here
N, K = list(map(int, input().split()))
li = list(map(int, input().split()))
if N == K:
    print((1))
    quit()
i = 1
N = N - K
while N >= K:
    N = N - K + 1
    i = i + 1
print((i + 1))

import sys

input = sys.stdin.readline
n, k = list(map(int, input().split()))
a = list(map(int, input().split()))
res = 1
cnt = k
if n <= cnt:
    print(res)
else:
    if (n - k) % (k - 1) == 0:
        print((1 + (n - k) // (k - 1)))
    else:
        print((1 + (n - k) // (k - 1) + 1))

-# your code goes here -N, K = list(map(int, input().split())) -li = list(map(int, input().split())) -if N == K: -    print((1)) -    quit() -i = 1 -N = N - K -while N >= K: -    N = N - K + 1 -    i = i + 1 -print((i + 1)) +import sys + +input = sys.stdin.readline +n, k = list(map(int, input().split())) +a = list(map(int, input().split())) +res = 1 +cnt = k +if n <= cnt: +    print(res) +else: +    if (n - k) % (k - 1) == 0: +        print((1 + (n - k) // (k - 1))) +    else: +        print((1 + (n - k) // (k - 1) + 1))