N = gets.to_f

if N == 0
    puts 0.4
    exit
end

y = N**(3/2.0)
coeffs = {
    0 => y,
    3 => 1 / (2*y),
    6 => -y / (8 * N**6),
    9 => y / (16 * N**9),
    12 => -5 * y / (128 * N**12),
    15 => 7 * y / (256 * N**15),
    18 => -21.0 * y / (1024 * N**18),
    21 => 33 * y / (2048 * N**21),
    24 => -429 * y / (32768 * N**24),
    27 => 715 * y / (65536 * N**27)
}

ans = 0.0
coeffs.each do |n, c|
    ans += c / (n + 1)
end

puts ans