Sum of numbers with max gcd.py

#!/bin/python3

import sys
from fractions import gcd
from itertools import product

def maximumGcdAndSum(A, B):
    gcd_max=0
    x_max=0
    y_max=0
    for x,y in product(A,B):
        z=gcd(x,y)
        if(z>gcd_max):
            gcd_max=z
            x_max=x
            y_max=y
        elif(z==gcd_max):
            s_new=x+y
            if(s_new>=(x_max+y_max)):
                x_max=x
                y_max=y
    sum=x_max+y_max
    return sum

if __name__ == "__main__":
    n = int(input().strip())
    list_A = list(map(int, input().strip().split(' ')))
    list_B = list(map(int, input().strip().split(' ')))
    A=list(set(list_A))
    B=list(set(list_B))
    res = maximumGcdAndSum(A, B)
    print(res)

Need to reduce the time complexity.