Greatest common divisor program using euclids algorithms

#Credits to NPTEL MOOC, Programming, Data Structures & Algorithms in 
#Python by Madhavan Mukund, Chennai Mathematical Institute 

def gcd(m,n):
    if m < n:
        (m,n) = (n,m)
    if (m%n) == 0:
        return(n)
    else:
        diff = m-n

        return(gcd(max(n,diff),min(n,diff)))

print(gcd(12,3))