Andrew Stankevich Contest 1 Problem A Python solution

n = int(open('china.in', 'r').readline())

half = n // 2

if n % 2 == 1:
    ans = half
elif (half - 1) % 2 == 1:
    ans = half - 1
else:
    ans = half - 2

open('china.out', 'w').write(str(ans))