import math,string,itertools,fractions,heapq,collections,re,array,bisect,sys,random,time



sys.setrecursionlimit(10**7)

inf=10**20

mod=10**9+7



def LI(): return list(map(int,input().split()))

def I(): return int(eval(input()))

def LS(): return input().split()

def S(): return eval(input())



def main():

  a,b=LI()

  l=LI()



  c=1

  _b=b

  while True:

    if a<=_b:

      break

    else:

      _b+=b-1

      c+=1



  return c



print((main()))

import math,string,itertools,fractions,heapq,collections,re,array,bisect,sys,random,time



sys.setrecursionlimit(10**7)

inf=10**20

mod=10**9+7



def LI(): return list(map(int,input().split()))

def I(): return int(eval(input()))

def LS(): return input().split()

def S(): return eval(input())



def main():

  n,k=LI()

  l=LI()



  c=1

  n-=k



  while True:

    if n<=0:

      break



    n-=(k-1)

    c+=1



  return c



print((main()))

import math, string, itertools, fractions, heapq, collections, re, array, bisect, sys, random, time

sys.setrecursionlimit(10**7)
inf = 10**20
mod = 10**9 + 7


def LI():
    return list(map(int, input().split()))


def I():
    return int(eval(input()))


def LS():
    return input().split()


def S():
    return eval(input())


def main():
    a, b = LI()
    l = LI()
    c = 1
    _b = b
    while True:
        if a <= _b:
            break
        else:
            _b += b - 1
            c += 1
    return c


print((main()))

import math, string, itertools, fractions, heapq, collections, re, array, bisect, sys, random, time

sys.setrecursionlimit(10**7)
inf = 10**20
mod = 10**9 + 7


def LI():
    return list(map(int, input().split()))


def I():
    return int(eval(input()))


def LS():
    return input().split()


def S():
    return eval(input())


def main():
    n, k = LI()
    l = LI()
    c = 1
    n -= k
    while True:
        if n <= 0:
            break
        n -= k - 1
        c += 1
    return c


print((main()))

-    a, b = LI() +    n, k = LI() -    _b = b +    n -= k -        if a <= _b: +        if n <= 0: -        else: -            _b += b - 1 -            c += 1 +        n -= k - 1 +        c += 1