let [| h; w |] = stdin.ReadLine().Split(" ") |> Array.map int64

let ans = 
  if h = int64 1 || w = int64 1 then
    int64 1
  else if h % int64 2 = int64 0 then 
    w * h / int64 2 
  else 
    w * (h - int64 1) / int64 2 + (w / int64 2) + int64 1   
ans |> printfn "%d"