def kaizyo(c)
    ans = 1
    return 1 if (c < 2)
    (2..c).each do |d|
        ans *= d
    end
    return ans
end
ans = 0
n = gets.chomp.to_i
pls = 1
(0..(n/2)).each do |d|
    ans += pls
    lose = d * 2
    pls = pls * (n - lose)
    pls = pls * (n - lose - 1)
    pls = pls/ (n - d) 
    pls /= (d+1) if(d > 0)
end
p ans