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 AtCoder
{
    class Program
    {
        public static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            string a = Console.ReadLine();
            string b = Console.ReadLine();
            string c = Console.ReadLine();

            int cnt = 0;
            for (int i = 0; i < n; i++)
            {
                string ai = a.Substring(i, 1);
                string bi = b.Substring(i, 1);
                string ci = c.Substring(i, 1);

                if (ai == bi && bi == ci)
                    continue;
                if (ai != bi && bi != ci && ci != ai)
                {
                    cnt = cnt + 2;
                    continue;
                }

                ++cnt;
            }

            Console.WriteLine(cnt);
        }
    }
}