output_description: Print Tak's total accommodation fee.
  
  * * *
input_description: The input is given from Standard Input in the following format:
  
      
      
      N
      K
      X
      Y
attempt: # 044_a
  # A - 高橋君とホテルイージー
  
  N = int(input())  # 連泊数
  K = int(input())  # 料金変動泊数
  X = int(input())  # 通常価格
  Y = int(input())  # 変動価格
  
  if (
      ((1 <= N & N <= 10000) & (1 <= K & K <= 10000))
      & (1 <= X & X <= 10000)
      & (1 <= Y & Y <= 10000)
  ):
      if X > Y:
          price = 0
          if N < K:
              for i in range(1, N + 1):
                  price += X
          if N >= K:
              for i in range(1, K + 1):
                  price += X
              for j in range(K + 1, N + 1):
                  price += Y
          print(price)
  
problem_description: Statement
  
  There is a hotel with the following accommodation fee:
  
    * X yen (the currency of Japan) per night, for the first K nights
    * Y yen per night, for the (K+1)-th and subsequent nights
  
  Tak is staying at this hotel for N consecutive nights. Find his total
  accommodation fee.
samples: [{"input": "5\n    3\n    10000\n    9000", "output": "48000\n    \n\nThe accommodation fee is as follows:\n\n  * 10000 yen for the 1-st night\n  * 10000 yen for the 2-nd night\n  * 10000 yen for the 3-rd night\n  * 9000 yen for the 4-th night\n  * 9000 yen for the 5-th night\n\nThus, the total is 48000 yen.\n\n* * *"}, {"input": "2\n    3\n    10000\n    9000", "output": "20000"}]