The last digit

LASTDIG
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 two numbers a and b. The problem consist in find 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.

CODE

import math
t=input()
for i in range(t):
    s=raw_input()
    str=s.split(' ')
    a=int(str[0])
    b=int(str[1])
    if(b==0):
        print 1
    else:
        a=a%10
        b=b%4
        if(b==0):
            b=4
        print pow(a,b)%10