#!/usr/bin/python

'''
Description:	Use sigmoid equation for logistic regression
Keywords:		sigmoid, logistic, logistic regression, 
				regression, pop, split
Example Input:	1.5 2 -1 -2.5 3
				2 -1 2 0.5
'''

e=2.7182818284590452353602874713527
C = str(raw_input())
X = str(raw_input())
C = C.split(" ")
X = X.split(" ")
x=float(C.pop())
for i in range(0, len(X)):
#	x = x+(float(C[i])*(float(X[i])**(float(len(X))-float(i))))
	x = x+(float(C[i])*float(X[i]))
	
print str(format(round(1/(1+(e**(-x))),3),'.3f'))