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;

class Program
{
  /// <summary>
  ///   The main entry point for the application
  /// </summary>
  [STAThread]
  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 count = 2 * n;
    for (int i = 0; i < n; i++)
    {
      if(a[i] == b[i] && b[i] != c[i]) count --;
      if(a[i] != b[i] && b[i] == c[i]) count --;
      if(a[i] != b[i] && a[i] == c[i]) count --;
      if(a[i] == b[i] && b[i] == c[i]) count -= 2;
    }
    Console.WriteLine(count);
  }
}