题目描述

Given a pair of positive integers, for example, 6 and 110, can this
equation 6 = 110 be true?  The answer is "yes", if 6 is a
decimal number and 110 is a binary number.





Now for any pair of positive integers N1 and N2, your task is to find
the radix of one number while that of the other is given.

输入描述:

Each input file contains one test case. Each case occupies a line which contains 4 positive integers:
N1 N2 tag radix
Here N1 and N2 each has no more than 10 digits.  A digit is less than its radix and is chosen from the set {0-9, a-z} where 0-9 represent the decimal numbers 0-9, and a-z represent the decimal numbers 10-35.  The last number "radix" is the radix of N1 if "tag" is 1, or of N2 if "tag" is 2.

输出描述:

For each test case, print in one line the radix of the other number so that the equation N1 = N2 is true.  If the equation is impossible, print "Impossible".  If the solution is not unique, output the smallest possible radix.

输入例子:

6 110 1 10

输出例子:

2
Sample Input 2:
1 ab 1 2
Sample Output 2:
Impossible