Problem:
Score : 200 points

Problem Statement

You are given a string s consisting of lowercase English letters. Extract all the characters in the odd-indexed positions and print the string obtained by concatenating them. Here, the leftmost character is assigned the index 1.

Constraints

Each character in s is a lowercase English letter.

1≤|s|≤10^5

Input

The input is given from Standard Input in the following format:

s

Output

Print the string obtained by concatenating all the characters in the odd-numbered positions.

Sample Input 1

atcoder

Sample Output 1

acdr

Extract the first character a, the third character c, the fifth character d and the seventh character r to obtain acdr.

Sample Input 2

aaaa

Sample Output 2

aa

Sample Input 3

z

Sample Output 3

z

Sample Input 4

fukuokayamaguchi

Sample Output 4

fkoaaauh

Solution in Haskell (GHC 7.10.3) (judge verdict: Accepted)

import Control.Monad.ST
import Data.STRef
import Data.Array.ST
import Control.Monad

main :: IO ()
main = do
  s <- getLine
  putStrLn $ oddString s

oddString :: String -> String
oddString str = runST $ do
  oddStr <- newSTRef ""
  arrStr <- newListArray (0, length str - 1) str :: ST s (STUArray s Int Char)
  forM_ [0..length str - 1] $ \i ->
    if i `mod` 2 == 1
      then return ()
      else do
        c <- readArray arrStr i
        now <- readSTRef oddStr
        writeSTRef oddStr (c:now)

  reverse <$> readSTRef oddStr