Hello! Please could you tell me how much I should spend to buy balls?

Hello,

I will try to explain my problem with an example. I want to buy 10 balls in a shop, spending the minimum money amount. In this shop, there are 2 balls at 1?, 3 balls at 2?, 4 balls at 3?, 4 balls at 5?, ..., 2 balls at 100?.
I want to know how much is the minimum that I should spend to buy these 10 balls.

Manually, I know that I have to spend 2*1?+3*2?+4*5?+1*5?=33?, but I don't know how to put this in an Excel Formula.
I have the number of balls for each price (from 1 to 100) in the column A1:A100. Column B could be the price (simply the sequence of numbers from 1 to 100). Obviously, I would have a solution not only for 10 balls but for n balls.

Could someone help me?

Thank you very much in advance,

Maurizio_V