**Problem Description**

For example, if M = 100.00, A = 4.00, F = 10, and a particular member visited the club 60 times during the year, then five of the 60 visits were free. The total cost to the member is 100.00 + 55 * 4.00 = 320.00 and the average cost per visit is 320.00 / 60 = 5.33 (rounded to the nearest cent).

**Input**

Each line of the input will contain data for one problem instance: positive values for M, A and F (defined above), and the actual number of visits V. M and A are positive floating point numbers (specified to two decimal places), F is a positive integer, and V is a non-negative integer. The end of input will be marked by end-of-file.

**Output**

For each line of input, the output will consist of the average cost per visit, displayed with a precision of two decimal places, i.e., rounded to the nearest cent.

**Sample Input**

100.00 4.00 10 60 100.00 4.00 10 55

**Sample Output**

5.33 5.45

**Source**

Rocky Mountain 2009