open Printf
open Scanf

let prod h w =
    if w mod 2 = 0 then (w/2)*h
    else if h mod 2 = 0 then (w/2)*(h/2)+(w+1)/2*h/2
    else (w/2)*(h/2)+(w+1)/2*(h+1)/2

let() = 
    scanf "%d %d" prod |> printf "%d\n"