Score : $100$ points

问题描述

高桥正在访问一家专门卖白菜的商店。

该商店以每颗白菜 $X$ 日元（日本货币）的价格出售。
但是，如果你一次性购买超过 $A$ 颗白菜，则第 $(A+1)$ 颗及以后的白菜将以每颗 $Y$ 日元的价格出售。
（保证 $Y \lt X$。参考样例输入/输出 1 以获取清晰理解。）

打印出购买 $N$ 颗白菜所需的金额。

以上为通义千问 qwen-max 翻译，仅供参考。

Problem Statement

Takahashi is visiting a shop specializing in cabbage.

The shop sells cabbage for $X$ yen (Japanese currency) per head.
However, if you buy more than $A$ heads of cabbage at once, the $(A+1)$-th and subsequent heads will be sold for $Y$ yen per head.
(It is guaranteed that $Y \lt X$. See Sample Input/Output 1 for clarity.)

Print the amount of money needed to buy $N$ heads of cabbage.

Constraints

• $1 \leq N \leq 10^5$
• $1 \leq A \leq 10^5$
• $1 \leq Y \lt X \leq 100$
• All values in input are integers.

Input

Input is given from Standard Input in the following format:

$N$ $A$ $X$ $Y$

Output

Print the amount of money needed to buy $N$ heads of cabbage (as an integer).

Sample Input 1

5 3 20 15

Sample Output 1

90

You need to pay $20$ yen for each of the $1$-st through $3$-rd heads of cabbage, and $15$ yen for each of the $4$-th and $5$-th heads of cabbage.
Thus, you need to pay a total of $20+20+20+15+15 = 90$ yen for the $5$ heads of cabbage.

Sample Input 2

10 10 100 1

Sample Output 2

1000

update @ 2024/3/10 09:23:56