257_A.hs

module Main where

import Data.List
import Control.Monad

qsort [] = []
qsort (x:xs) = qsort more ++ [x] ++ qsort less
      where
      (less, more) = partition (< x) xs

solveM :: Int -> Int -> [Int] -> Maybe Int
solveM 0 0 _ = Just 0
solveM _ 0 _ = Nothing
solveM m k [] = if m > k
                  then Nothing
                  else Just 0
solveM m k (x:xs) = if m > k
                      then liftM2 (+) (Just 1) (solveM m (k+x-1) xs)
                      else Just 0

solve :: Int -> Int -> [Int] -> Int
solve m k xs = fromMaybe (-1) (solveM m k xs)

main = do
     nmkStr <- getLine
     let [_, m, k] = map read $ words nmkStr
     electricStr <- getLine
     let electric = qsort $ map read $ words electricStr
     print $ solve m k electric