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 != 2:
			month += 1
			day = day-days_per_month[month-2]
		elif day > 29 and month == 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 == 1:
		sundays += 1

print(sundays)