소스 코드 제출

# h=int(input())

# n=[]

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

# k=(h)

# for y in range(0, h):

# for x in range(y, k):

# if x > (h-1):

# print(n[x-h], end=' ')

# else:

# print(n[x], end=' ')

# print(end=' ')

# print()

# k+=1

# a = int(input())

# k=a

# b = int(input())

# c=[]

# c=list(map(int, input().split()))

# for x in range(0, b):

# a=a*(100+c[x])/100

# f=a-k

# print(round(f))

# if round(f)>0:

# print('good')

# elif (a-k)==0:

# print('same')

# else:

# print('bad')

(a, m, d, n)=map(int, input().split())

for x in range(1, n):

  if x % 2 ==0:

    a=a+d

  else:

    a=a*m

print(a)