#!/usr/bin/env python3

from fractions import Fraction

def search(turns, wins=0, discs=2, cache={}):
    if discs - 2  == turns:
        return 2* wins > turns
    if  turns // 2 - wins > turns - discs + 1:
        return 0
    if (discs, wins) in cache:
        return cache[(discs, wins)]
    r = Fraction(1, discs) * search(turns, wins+1, discs+1)
    r += Fraction(discs-1, discs) * search(turns, wins, discs+1)
    cache[(discs, wins)] = r
    return r

N = 15
print(int(search(N)**(-1)))