let C = decimal<|stdin.ReadLine()
let a = Array.map decimal <| stdin.ReadLine().Split(' ')
if C = 0M then printfn "0.0000000000"
else
    let P = 3.1415926536M
    let r = (a.[1] - a.[0])/2M
    let R = r + a.[0]
    printfn "%M" <| 2M*P*P*r*r*R*C