def gcd(a,b):
    if a < b:
        a,b = b,a
    while b:
        a,b = b,a%b
    return a
import math
assert gcd(13, 2436) == 1
assert gcd(10, 2) == 2
assert math.gcd(13, 2436) == 1
assert math.gcd(10, 2) == 2