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


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