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: (N,) = list(map(int, input().split()))
  (K,) = list(map(int, input().split()))
  (X,) = list(map(int, input().split()))
  (Y,) = list(map(int, input().split()))
  print(X * min(K, N) + Y * max(0, N - K))
  
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"}]