Recall of a Spam Classifier

Security at Larkspur Mail is asking the opposite question from the support team. They do not care what is sitting in the junk folder; they care how much spam reached a customer's inbox, because that is where the phishing links get clicked. They read the same bake-off runs the support team does, one candidate build at a time.

Throughout, spam is the positive class - a "positive" means the filter raised the alarm.

Task: Print the filter's recall for the spam class - also called sensitivity, or the true positive rate - as a single number rounded to 4 decimals. Round once, at the end.

Input

Four lines, each holding one whole number from a single evaluation run, in this order:

1. spam, and the filter flagged it.
2. real mail, and the filter flagged it anyway.
3. real mail, and the filter let it through.
4. spam, and the filter let it through.

Every run contains at least one genuinely spam email.

Output

One line holding the recall rounded to 4 decimals, printed the way Python prints a float - 0.75, never 0.7500.

Example:

Input:
40
10
45
5

Output:
0.8889