# Problem Q: Problem Q: Health

Source: `health.{c,cpp,java}`
Input: `console {stdin,cin,System.in}`
Output: `console {stdout,cout,System.out}`

Annual membership at a health club costs `M` dollars. In addition to the annual membership fee, members are normally charged an admission of `A` dollars upon each visit. After `F` visits, however, members are entitled to one free admission.

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