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)?

```
def isleap(year):
if not year%100:
if not year%400:
return 29
return 28
if not year%4:
return 29
return 28
ans = 0
days = sum([31,isleap(1900),31,30,31,30,31,31,30,31,30,31])
for y in range(1, 101):
month = 0
for m in [0,31,isleap(1900+y),31,30,31,30,31,31,30,31,30]:
month += m
if not (days+1+month)%7:
ans += 1
days += sum([31,isleap(1900+y),31,30,31,30,31,31,30,31,30,31])
print(ans)
```