let ``No.729 文字swap``() =

  stdin.ReadLine()
  |> fun s ->

    let i, j =
      stdin.ReadLine().Split(' ')
      |> Array.map (int)
      |> fun args -> args.[0], args.[1]

    let builder = System.Text.StringBuilder(s)
    let ic = s.[i]
    let jc = s.[j]
    builder.Remove(i, 1)  |> ignore
    builder.Insert(i, jc) |> ignore
    builder.Remove(j, 1)  |> ignore
    builder.Insert(j, ic) |> ignore
    builder.ToString() |> stdout.WriteLine 

  ()
``No.729 文字swap``()