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: Accepted)

main = do
  n <- getLine
  s1 <- getLine
  s2 <- getLine
  s3 <- getLine
  putStrLn . show $ solve (s1,s2,s3)

solve :: (String,String,String) -> Int
solve ([],_,_) = 0
solve ((c1:s1), (c2:s2), (c3:s3)) = (compare3 c1 c2 c3) + solve (s1,s2,s3)


compare3 :: Char -> Char -> Char -> Int
compare3 a b c
  | a == b && b == c = 0
  | a == b && b /= c = 1
  | b == c && a /= b = 1
  | c == a && a /= b = 1
  | otherwise = 2