# -*- coding: utf-8 -*- # Created by Ross on 19-4-12 n = int(input()) if n < 1:     exit() neg = 1  # 表示前面两人都抽不中的概率 c = 0 ps = [] for i in range(n):     p = float(input())     ps.append(p) i = 0 while i < 100:     if i % 2 == 0:  # 轮到小明         p = ps[i % n]         c += neg * p         neg *= (1 - p)     else:  # 轮到小华         p = ps[i % n]         neg *= 1 - p     i += 1 print('%.4f' % c)