import strutils, sequtils, math

var
  c, ri, ro: float

c = stdin.readLine.parseFloat
var scan = stdin.readLine.split.map(parseFloat)
ri = scan[0]
ro = scan[1]

# (ΦωΦ)＜パップス＝ギュルダン
var res: float = c*PI*PI*(ro+ri)*(ro-ri)*(ro-ri) / 4
echo res