package main

import . "fmt"
import . "math"

func main() {
	var c,rin,rout float64
	Scan(&c,&rin,&rout)
	// V=2*(pi*pi)*(r*r)*R
	r:=(rout-rin)/2
	R:=(rout+rin)/2
	v:=2*Pi*Pi*r*r*R
	Printf("%.10f\n",c*v)
}