import strutils, sequtils

when isMainModule:
  var
    x = stdin.readline.parsefloat
    ans = 0.0
  let p = 1.6449340668482426
  for i in 1..1000000:
    ans -= x*(2*i.float+x) / (i.float*i.float*(i.float+x)*(i.float+x))
  echo ans + p