let (|ZERO|ODD|EVE|) n = 
    match n%2,n with
    | _,0 -> ZERO
    | 0,x -> EVE x
    | _,x -> ODD x

let genTakableEdgeLengthList = function
    | ZERO  -> [0]
    | ODD x -> [1 .. (x/2)+1]
    | EVE x -> [1 .. (x/2)  ] 

let D = stdin.ReadLine() |> int

D/2
|> genTakableEdgeLengthList
|> List.map (fun x -> x * (D/2-x))
|> List.max
|> printfn "%i"