let [| n; k |] =
    stdin.ReadLine().Split()
    |> Array.map int

let g =
    Array.init (n + 1) (fun _ -> [])

for i = 1 to n - 1 do
    let [| a; b |] =
        stdin.ReadLine().Split()
        |> Array.map int

    g.[a] <- b :: g.[a]
    g.[b] <- a :: g.[b]

let seen =
    Array.zeroCreate<bool> <| n + 1

let dist =
    Array.init (n + 1) (fun _ -> [])

dist.[0] <- [ 1 ]

let mutable ans = 0
let mutable coin = k

if n >= k then
    for d in 0 .. n - 1 do
        for x in dist.[d] do
            if coin > 0 && not seen.[x] then
                seen.[x] <- true
                dist.[d + 1] <- dist.[d + 1] @ g.[x]
                ans <- ans + d
                coin <- coin - 1
else
    ans <- -1

ans
|> printfn "%d"