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 Ruby (2.3.3) (judge verdict: Accepted)

lengthOfStrings = gets.to_i - 1
firstStrings  = gets.to_s
secondStrings = gets.to_s
thirdStrings  = gets.to_s

timesOfExchange = 0

for index in 0..lengthOfStrings do
    letterOfEachStrings = []
    letterOfEachStrings << firstStrings[index]
    letterOfEachStrings << secondStrings[index]
    letterOfEachStrings << thirdStrings[index]


    letterOfEachStrings =  letterOfEachStrings.uniq

    if letterOfEachStrings.size == 3 then
        timesOfExchange = timesOfExchange + 2
    elsif letterOfEachStrings.size == 2 then
        timesOfExchange = timesOfExchange + 1
    elsif letterOfEachStrings.size == 1 then
        timesOfExchange = timesOfExchange
    end
end

puts timesOfExchange