Problem:
Score : 200 points

Problem Statement

You are given three strings A, B and C. Each of these is a string of length N consisting of lowercase English letters.

Our objective is to make all these three strings equal. For that, you can repeatedly perform the following operation:

Operation: Choose one of the strings A, B and C, and specify an integer i between 1 and N (inclusive). Change the i-th character from the beginning of the chosen string to some other lowercase English letter.

What is the minimum number of operations required to achieve the objective?

Constraints

1 \leq N \leq 100

Each of the strings A, B and C is a string of length N.

Each character in each of the strings A, B and C is a lowercase English letter.

Input

Input is given from Standard Input in the following format:

N
A
B
C

Output

Print the minimum number of operations required.

Sample Input 1

4
west
east
wait

Sample Output 1

3

In this sample, initially A = west、B = east、C = wait. We can achieve the objective in the minimum number of operations by performing three operations as follows:

Change the second character in A to a. A is now wast.

Change the first character in B to w. B is now wast.

Change the third character in C to s. C is now wast.

Sample Input 2

9
different
different
different

Sample Output 2

0

If A, B and C are already equal in the beginning, the number of operations required is 0.

Sample Input 3

7
zenkoku
touitsu
program

Sample Output 3

13

Solution in Haskell (GHC 7.10.3) (judge verdict: Wrong Answer)

import Control.Monad
import Data.List
import Control.Applicative

main = do
  n <- readLn
  [a,b,c] <- replicateM 3 getLine
  putStrLn $ show $ cnt a b c n

cnt :: [Char] -> [Char] -> [Char] -> Int -> Int
cnt (a:as) (b:bs) (c:cs) n
  |n <= 0 = 0
  |((a:as) == (b:bs)) && ((b:bs) == (c:cs)) = 0
  |length (filter (== a) [b,c]) == 1 = (+) 1 $ cnt as bs cs (n -1)
  |(b == c) = (+) 1 $ cnt as bs cs (n -1)
  |otherwise =  (+) 2 $ cnt as bs cs (n -1)
cnt _ _ _ 0 = 0