3 人解决，9 人已尝试。
3 份提交通过，共有 19 份提交。
9.0 EMB 奖励。
单点时限: 2.0 sec
内存限制: 256 MB
Professor Octastichs has invented a new programming language, Smeech. An expression in Smeech may be a positive or negative integer, or may be of the form (p e1 e2) where p is a real number between 0 and 1 (inclusive) and e1 and e2 are Smeech expressions. The value represented by a Smeech expression is as follows:
An integer represents itself
With probability p, (p e1 e2) represents x + y where x is the value of e1 and y is the value of e2; otherwise it represents x - y.
Given a Smeech expression, what is its expected value?
Input consists of several Smeech expressions, one per line, followed by a line containing ().
For each expression, output its expected value to two decimal places.
7 (.5 3 9) ()
7.00 3.00
3 人解决，9 人已尝试。
3 份提交通过，共有 19 份提交。
9.0 EMB 奖励。