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;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace TheSecondHeat
{
    class Program
    {
        static void Main(string[] args)
        {
            // 整数の入力
            int N = int.Parse(Console.ReadLine());
            // スペース区切りの整数の入力
            //string[] input = Console.ReadLine().Split(' ');
            //int b = int.Parse(input[0]);
            //int c = int.Parse(input[1]);
            // 文字列の入力
            string A = Console.ReadLine();
            string B = Console.ReadLine();
            string C = Console.ReadLine();

            int ans = 0;
            for(var i = 0; i < N; i++)
            {
                if(A.Substring(i,1) != B.Substring(i, 1))
                {
                    ans++;
                }
                if (A.Substring(i, 1) != C.Substring(i, 1))
                {
                    ans++;
                }
                if ((B.Substring(i, 1) == C.Substring(i, 1))&&(A.Substring(i, 1) != B.Substring(i, 1)))
                {
                    ans--;
                }
            }
            if (ans < 0)
            {
                ans = 0;
            }
            //出力
            Console.WriteLine(ans);
        }
    }
}