open System

let rec gcd a b =
    match b with 
    | 0 -> a
    | _ -> gcd b (a%b)

let N,K = 
    let t = Console.ReadLine().Split()
            |> Array.map(int)
    t.[0],t.[1]

[1..N-1]
|> List.map (fun x -> gcd x (N-x))
|> List.max
|> printfn "%i"