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Without datetime solution in Clear category for Unlucky Days by ciel
def zeller(_y,m,d):
m+=1
if m<4: _y-=1;m+=12
y=_y//100
z=_y%100
return (5*y+z+y//4+z//4+13*m//5+d-1)%7
checkio=lambda y: sum(zeller(y,m,13)==5 for m in range(1,13))
if __name__ == '__main__':
assert checkio(2015) == 3, "First - 2015"
assert checkio(1986) == 1, "Second - 1986"
March 2, 2016
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