The number of steps

Time Limit: 1000 ms Memory Limit: 65536 KiB

Problem Description

    Mary stands in a strange maze, the maze looks like a triangle(the first layer have one room,the second layer have two rooms,the third layer have three rooms …). Now she stands at the top point(the first layer), and the KEY of this maze is in the lowest layer’s leftmost room. Known that each room can only access to its left room and lower left and lower right rooms .If a room doesn’t have its left room, the probability of going to the lower left room and lower right room are a and b (a + b = 1 ). If a room only has it’s left room, the probability of going to the room is 1. If a room has its lower left, lower right rooms and its left room, the probability of going to each room are c, d, e (c + d + e = 1). Now , Mary wants to know how many steps she needs to reach the KEY. Dear friend, can you tell Mary the expected number of steps required to reach the KEY?


Input

There are no more than 70 test cases. 
 
In each case , first Input a positive integer n(0
The input is terminated with 0. This test case is not to be processed.

Output

Please calculate the expected number of steps required to reach the KEY room, there are 2 digits after the decimal point.

Sample Input

3
0.3 0.7
0.1 0.3 0.6
0 

Sample Output

3.41

Hint

 

Source

2013年山东省第四届ACM大学生程序设计竞赛