package main

import (
    "fmt"
    "math"
)

func main() {
    var c, rIn, rOut float64
    fmt.Scan(&c, &rIn, &rOut)

    r := (rOut - rIn) / 2.0
    s := r * r * math.Pi

    fmt.Println(c * s * (rIn + r) * 2 * math.Pi)
}