def mort(amt, years, rate):
    ffactor = (1 + rate / 2) ** (1 / 6.0)
    pow = ffactor ** (12 * years)
    monthly = amt * pow * (ffactor -1) / ( pow - 1)
    return monthly


a = 40000
y = 25
r = 0.05
print mort(a, y, r)