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;
             
public static class Program
{
    public static void Main()
    {
        int N = GetInt();
        string A = ReadLine();
        string B = ReadLine();
        string C = ReadLine();
        int count = 0;
        for (int i = 0; i < N; i++)
        {
            if (A[i] == B[i])
            {
                if (A[i] != C[i]) ++count;
            } else if (A[i] == C[i]) {
                ++count;
            } else if (B[i] == C[i]) {
                ++count;
            } else {
                count += 2;
            }
        }
        Console.WriteLine(count.ToString());
    }
    
    private static string ReadLine()
    {
    	return Console.In.ReadLine();
    }
    
    public static int[] GetIntArray()
    {
    	List<int> temp = new List<int>();
    	foreach (string c in ReadLine().Split(' '))
            temp.Add(int.Parse(c));
        return temp.ToArray();
    }
    
    public static int GetInt()
    {
    	return int.Parse(ReadLine());
    }
}