package main

import (
	"fmt"
	"math"
)

func resolve(C, Rin, Rout float64) float64 {
	r1 := (Rout - Rin) / 2
	r2 := (Rout + Rin) / 2
	res := C * math.Pi * math.Pow(r1, 2) * (2 * math.Pi * r2)
	return res
}

func main() {
	var C, Rin, Rout float64
	fmt.Scanf("%f\n", &C)
	fmt.Scanf("%f %f\n", &Rin, &Rout)
	fmt.Println(resolve(C, Rin, Rout))
}