Dismath

def modexp(a, n, m):
    b = []
    while n:
        b.append(n%2)
        n /= 2
    power = 1
    b.reverse()
    for x in b:
        power = (power*power)%m
        if x:
            power = (power*a)%m
    return power

print (modexp (2,34, pow(10,10)))
print (modexp (2,pow(10,20), pow(10,10)))