from __future__ import print_function
'''
Counting Sundays
Problem 19
You are given the following information, but you may prefer to do some research for yourself.
1 Jan 1900 was a Monday.
Thirty days has September,
April, June and November.
All the rest have thirty-one,
Saving February alone,
Which has twenty-eight, rain or shine.
And on leap years, twenty-nine.
A leap year occurs on any year evenly divisible by 4, but not on a century unless it is divisible by 400.
How many Sundays fell on the first of the month during the twentieth century (1 Jan 1901 to 31 Dec 2000)?
'''
days_per_month = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
day = 6
month = 1
year = 1901
sundays = 0
while year < 2001:
day += 7
if (year%4 == 0 and not year%100 == 0) or (year%400 == 0):
if day > days_per_month[month-1] and month is not 2:
month += 1
day = day-days_per_month[month-2]
elif day > 29 and month is 2:
month += 1
day = day-29
else:
if day > days_per_month[month-1]:
month += 1
day = day-days_per_month[month-2]
if month > 12:
year += 1
month = 1
if year < 2001 and day is 1:
sundays += 1
print(sundays)