open System
open System.Text

let separateStr (arg:string) =
  let rec splitStr (acc:StringBuilder) (argStr:StringBuilder) =
  
    if argStr.Length <= 3
    then argStr.ToString() + acc.ToString()
    else
        acc.Insert(0,argStr.Chars (argStr.Length-1))
        acc.Insert(0,argStr.Chars (argStr.Length-2))
        acc.Insert(0,argStr.Chars (argStr.Length-3))
        acc.Insert(0, ',' )
        argStr.Length <- argStr.Length-3
        splitStr  acc argStr 
             
  splitStr (new StringBuilder()) (new StringBuilder(arg))
  
Console.ReadLine() 
|> separateStr  
|> Console.WriteLine