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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;

namespace B__Touitsu
{
    class Program
    {
        static void Main(string[] args)
        {
            int N = int.Parse(Console.ReadLine());

            char[][] s = new char[3][];
            s[0] = Console.ReadLine().ToCharArray();
            s[1] = Console.ReadLine().ToCharArray();
            s[2] = Console.ReadLine().ToCharArray();

            int Count = 0;

            for(int i=0;i<N;i++)
            {
                if (s[0][i] == s[1][i])
                {
                    if (s[0][i] == s[2][i])
                        Count += 0;
                    else
                        Count += 1;
                } 
                else
                {
                    if (s[1][i] == s[2][i] || s[0][i] == s[2][i])
                        Count += 1;
                    else
                        Count += 2;
                }

            }

            Console.WriteLine(Count.ToString());
        }
    }
}