[<EntryPoint>]
let main argv =
    let input = stdin.ReadLine().Split(' ') |> Array.map int64
    let h = input.[0]
    let w = input.[1]
    let count =
        if  h = 1L || w = 1L then 1L
        else (h * w + 1L) / 2L
    count |> printfn "%d"
    0
