fun readLargeInt () =
    valOf (TextIO.scanStream (LargeInt.scan StringCvt.DEC) TextIO.stdIn)


val () =
    let
        val x = readLargeInt ()
        val y = readLargeInt ()
        val d = readLargeInt ()

        val shorter = LargeInt.min (x, y)
        val longer = LargeInt.max (x, y)
        val dd = LargeInt.min (d, x + y - d)
                
        val ans = if dd < 0 then 0
                  else if dd <= shorter then dd + 1
                  else shorter + 1
    in    
        print (LargeInt.toString ans ^ "\n")
    end