我有一个有限的对象供应并作为对象购买，价格上升。因此在N（每N个对象都买，价格上涨的时间）组。当试图购买的对象，什么是计算总成本的最简单的方法是什么？

I have a limited supply of objects and as the objects are purchased, the price goes up accordingly in groups of N (every time N objects are bought, price increases). When trying to purchase a number of objects, what is the easiest way to calculate total cost?

例： 我有24个富。对于每一个N（例如使用3）被购买，价格增加1 所以，如果我买1为1的价格则有23个左右，2人给出在1 价格 1已经购买了之后，有人希望购买6井的总成本是=（2 * 1）+（3×2）+（1 * 3）

Example: I have 24 foo. For every N(example using 3) that are purchased, the price increases by 1. So if I buy 1 at the prices of 1 then there are 23 left and 2 left at the price of 1. After 1 has been purchased, someone wishes to buy 6. Well the total cost would be = (2*1)+(3*2)+(1*3)

推荐答案

OK，我认为这是正确的，现在......

OK, I think that this is correct now...

由于：

X  = Total Number of Items Bought
N  = Number of Items per Price Increment
B  = Base Item Price, before any Increments
I  = Price Increment per [N]

设置：

J  = FLOOR((X-1)/N)+1

然后：

TotalCost = X*(B-I) + I*(X*J - N*J*(J-1)/2)