Archit loves to challenge people for different tasks but this time Pulkit challenged him with a task.
The task was that given two distinct strings A and B you have to make another string C of the same length as A, by arranging the characters of string A in such a manner it is a lexicographically largest possible string which is strictly smaller than string B.
As Archit is busy playing counter strike, he has asked for your help to win the challenge.
Note: It is not necessary that the length of both the strings A and B is the same.
INPUT: The first line of input contains a single integer T denoting the number of test cases. Next 2T lines follow each test case contains two lines the first line contains the string A and the second line contains string B.
OUTPUT: For each test case print a single line containing the string C(in lowercase), and if no such string C is possible then print "IMPOSSIBLE"(without quotes).
CONSTRAINTS:
1<=T<=10.
1<=|A|,|B|<=100.
where |X| denotes the length of the Xth String.
All possible strings that can be formed by the arrangement of the character of string A, and are strictly less than string B are as follows:
abcd, abdc, acbd, acdb, adcb, adbc, bacd, badc.
Among these the lexicographically largest is badc, which is the answer.
