import Control.Monad
import Data.Maybe
import qualified Data.ByteString.Char8 as BS
import Data.List
import Data.Char

readInt = fst . fromJust . BS.readInt
readIntList = map readInt . BS.words
getInt = readInt <$> BS.getLine
getIntList = readIntList <$> BS.getLine

main = do
    [n, k] <- getIntList
    s <- getLine
    putStr $ take (k - 1) s
    putChar . toLower . head $ drop (k - 1) s
    putStrLn $ drop k s