Problem:
Problem B: Cleaning Robot

Dr. Asimov, a robotics researcher, loves to research, but hates houseworks and his house were really dirty. So, he has developed a cleaning robot.

As shown in the following figure, his house has 9 rooms, where each room is identified by an alphabet:

The robot he developed operates as follows:

If the battery runs down, the robot stops.

If not so, the robot chooses a direction from four cardinal points with the equal probability, and moves to the room in that direction. Then, the robot clean the room and consumes 1 point of the battery.

However, if there is no room in that direction, the robot does not move and remains the same room. In addition, there is a junk room in the house where the robot can not enter, and the robot also remains when it tries to enter the junk room. The robot also consumes 1 point of the battery when it remains the same place.

A battery charger for the robot is in a room. It would be convenient for Dr. Asimov if the robot stops at the battery room when its battery run down.

Your task is to write a program which computes the probability of the robot stopping at the battery room.

Input

The input consists of several datasets. Each dataset consists of:

n
s t b

n is an integer that indicates the initial battery point. s, t, b are alphabets respectively represent the room where the robot is initially, the battery room, and the junk room.

The input ends with a dataset which consists of single 0 for n. Your program should not output for this dataset.

Output

For each dataset, print the probability as a floating point number in a line. The answer may not have an error greater than 0.000001.

Constraints

Judge data includes at most 100 data sets.

n ≤ 15

s, t, b are distinct.

Sample Input

1
E A C
1
E B C
2
E A B
0

Output for the Sample Input

0.00000000
0.25000000
0.06250000

Solution in Python (judge verdict: Wrong Answer)

time = -1
place = ["a","b","c","d","e","f","g","h","i"]
empty_count={}
for i in place:
	empty_count[i] = 0
count_d = empty_count.copy()	

def reset():
	global d
	global count_d
	d={"a":["a","a","b","d"],"b":["a","e","c","b"],"c":["b","f","c","c"],"d":["a","e","g","d"],"e":["b","d","f","h"],"f":["c","e","i","f"],"g":["d","h","g","g"],"h":["g","e","i","h"],"i":["f","h","i","i"]}
	count_d = empty_count.copy()
	print count_d,"reset"
	
def pre_set(start_place,fix_place):
	global d
	global count_d
	for i in place:
		d[i] = list(("").join(d[i]).replace(fix_place,i))
	count_d[start_place] = 1
	print count_d,"preset"
def repeat(time):
	global count_d
	for i in range (time):
		new_count_d = empty_count.copy()
		old_count_d = count_d.copy()
		for j in place:
			for k in d[j]:
				new_count_d[k] += old_count_d[j]
		print count_d,"repeat",i
		count_d = new_count_d.copy() 

while time != 0:
	time = int(raw_input())
	if time == 0:
		break
	else:
		info_pre = raw_input().split()
		info = []
		for i in info_pre:
			info.append(i.lower())
		
	reset()
	pre_set(info[0],info[2])
	repeat(time)
	print (count_d[info[1]])/float((4**time)),count_d[info[1]],float((4**time))