import math, sequtils, strformat, strutils
let
  c: int = stdin.readline.parseInt
  r: seq[int] = stdin.readline.split.map(parseInt)
  rad: float = (r[1] - r[0]) / 2
  ans: float = 2 * PI * PI * rad * rad * (r[0].float + rad) * c.float
echo fmt"{ans:.10f}"