package main

import (
	"fmt"
	"math"
)

func main() {
	var c, rin, rout float64
	fmt.Scan(&c)
	fmt.Scan(&rin, &rout)
	a := (rout-rin)/2.
	b := rout - a
//	fmt.Println(a, b, math.Pi, c)
	fmt.Println(a*a*b*math.Pi*math.Pi*2*c)
}