Please check what’s wrong with my code, it’s shows error when submitted on codechef

The question for the code:
Miss Ural wants to buy colors for Holi, and that too, at the cheapest cost!
There are N shops selling colors near Ural’s house, where the i′th shop sells colors at rate of Ri for one unit. Also, i′th shop is located at a distance of Di kilometers from her house. Life was simple, but then petrol and fuel prices soared up. The current price of petrol to travel one kilometer is K

Find the minimum cost at which Miss Ural can buy one unit of color. she does not need to return back home.

The first line of input contains T, number of test cases in a file.
The next line contains two integers, N and K, as described in the problem statement.
The next line contains N space separated integers, denoting Di, i.e. distance of the shop.
The next line contains N space separated integers denoting Ri, i.e. rate of the color.

For test case, output minimum cost to purchase 1 unit of color.
1≤T≤10^5
1≤N≤10^5
Sum of N over all T in a test file does not exceed 10^6.
1≤Ri,K,Di≤10^9