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 touitsu {
    class Program {
        static void Main(string[] args) {

            var length = int.Parse(Console.ReadLine());

            var strA = Console.ReadLine().Trim().ToList();
            var strB = Console.ReadLine().Trim().ToList();
            var strC = Console.ReadLine().Trim().ToList();

            var count = 0;

            for (int i = 0; i < length; i++) {
                if (strA[i].CompareTo(strB[i]) == 0) {
                    if (strA[i].CompareTo(strC[i]) == 0) {
                        // 全一緒
                    }
                    else {
                        // A equal B not C
                        strC[i] = strA[i];
                        count++;
                    }
                }
                else {
                    // A not B
                    if (strA[i].CompareTo(strC[i]) == 0) {
                        // A = C / B
                        strB[i] = strA[i];
                        count++;
                    }
                    else {
                        // A / (B C)
                        if (strB[i].CompareTo(strC[i]) == 0) {
                            // A / B = C
                            strA[i] = strB[i];
                            count++;
                        }
                        else {
                            //　全部違う
                            strA[i] = strB[i] = strC[i];
                            count += 2;
                        }
                    }
                }
            }
            Console.WriteLine(count);
            // Console.ReadLine();
        }
    }
}