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
