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A9621 | $Cheap Travel$

时间限制1s

内存限制256MB

通过 / 提交0/0

题目描述

Ann has recently started commuting by subway. We know that a one ride subway ticket costs $a$ rubles. Besides, Ann found out that she can buy a special ticket for $m$ rides (she can buy it several times). It costs $b$ rubles. Ann did the math; she will need to use subway $n$ times. Help Ann, tell her what is the minimum sum of money she will have to spend to make $n$ rides?

输入格式

The single line contains four space-separated integers $n$ , $m$ , $a$ , $b$ ( $1<=n,m,a,b<=1000$ ) — the number of rides Ann has planned, the number of rides covered by the $m$ ride ticket, the price of a one ride ticket and the price of an $m$ ride ticket.

输出格式

Print a single integer — the minimum sum in rubles that Ann will need to spend.

输入输出样例

输入 #1

6 2 1 2

输出 #1

输入 #2

5 2 2 3

输出 #2

C++ 编辑器

输入

输出