BestCoder 1st Anniversary ($)HDU5310 Souvenir 简单数学题

Souvenir

Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 262144/262144 K
(Java/Others)

Total Submission(s): 1146 Accepted Submission(s): 655



Problem Description

Today is the 1st anniversary of BestCoder. Soda, the contest manager, wants to buy a souvenir for each contestant. You can buy the souvenir one by one or set by set in the shop. The price for a souvenir is p yuan
and the price for a set of souvenirs if q yuan.
There's m souvenirs
in one set.

There's n contestants
in the contest today. Soda wants to know the minimum cost needed to buy a souvenir for each contestant.

Input

There are multiple test cases. The first line of input contains an integer T (1≤T≤105),
indicating the number of test cases. For each test case:

There's a line containing 4 integers n,m,p,q (1≤n,m,p,q≤104).

Output

For each test case, output the minimum cost needed.

Sample Input

2
1 2 2 1
1 2 3 4

Sample Output

1
3

Hint
For the first case, Soda can use 1 yuan to buy a set of 2 souvenirs.
For the second case, Soda can use 3 yuan to buy a souvenir.

Source

BestCoder 1st Anniversary ($)

出题人：本题是一个简单的数学题. 如果套装优惠的话就尽量买套装, 否则单件买.

注意一下如果一直用套装的话可能在最后的零头不如单买好, 即(n
\text{ mod } m) \cdot p < q(n mod m)⋅p<q.