Solve in Python:
_Friday 13th or Black Friday is considered as unlucky day. Calculate how many unlucky days are in the given year._

Find the number of Friday 13th in the given year.

__Input:__ Year as an integer.

__Output:__ Number of Black Fridays in the year as an integer.

__Examples:__

        unluckyDays(2015) == 3
        unluckyDays(1986) == 1

***Note:*** In Ruby years will start from 1593.
def unlucky_days(y):    
    count = 0 # Clean & Pure Math Example      
    for m in range(3,15):
        if m == 13: y-=1            
        if (y%100+(y%100//4)+(y//100)//4-2*(y//100)+26*(m+1)//10+12)%7==5:
            count += 1
    return count