LASTDIG  The last digit
Nestor was doing the work of his math class about three days but he is tired of make operations a lot and he should deliver his task tomorrow. His math’s teacher gives him two numbers a and b. The problem consist of finding the last digit of the potency of base a and index b. Help Nestor with his problem. You are given two integer numbers: the base a (0 <= a <= 20) and the index b (0 <= b <= 2,147,483,000), a and b both are not 0. You have to find the last digit of a^{b}.
Input
The first line of input contains an integer t, the number of test cases (t <= 30). t test cases follow. For each test case will appear a and b separated by space.
Output
For each test case output an integer per line representing the result.
Example
Input: 2 3 10 6 2
Output: 9 6
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wolv_dhoni:
20180410 07:41:19
It can be solved in O(1), all you have to do is calculate the last digit of a, a^2, a^3, a^4, after that it just keeps on repeating, you can check it on your own. 

flyer2403:
20180322 16:40:33
Last edit: 20180322 16:41:21 

jmr99:
20180311 10:32:34
ac in 2 go !! gys use string and consider 700 b limitation. 

badasshackme:
20180310 15:21:52
700 B limit is annoying. 

venkat016:
20180110 22:31:21
Modular exponenention _/\_ thanks for @ajayc1007 and @prasad_235 

vaibhavcs99:
20171231 08:16:40
AC after two TLE (I was using pow function).Modular exponention does the work.No need to consider when one of them is 0 cases. 

jaykay12:
20171230 20:57:42
Check


mayank1208_:
20171230 10:54:11
solved after 5 WA.but got AC in d end.... 

sgarg367:
20171203 19:07:48


justinegeo96:
20171125 13:50:18
should i check for negative values for a and b? Why am I getting WA :/ I am getting correct output using fast modular exponentiation. 
Added by:  Jose Daniel Rodriguez Morales 
Date:  20081201 
Time limit:  1s 
Source limit:  700B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: GOSU 
Resource:  Own 