#! /usr/bin/env stack
-- stack --resolver lts-12.20 --install-ghc script
{-# LANGUAGE ViewPatterns #-}
module Main where

import qualified Data.Char as C
import qualified Data.List as L

main :: IO ()
main = interact $ show . length . react . takeWhile C.isAlpha

react [] = []
react (x:(react -> ys))
   | (y:ys') <- ys, x `reactsWith` y = ys'
   | otherwise                       = x:ys

x `reactsWith` y = (C.isUpper x && C.toLower x == y) ||
                   (C.isLower x && C.toUpper x == y)