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 Python (3.4.3) (judge verdict: Accepted)

import sys
import collections


def r(n, a, b, c):

    cnt = 0
    for i in range(len(a)):
        cn = collections.Counter([a[i], b[i], c[i]])
        cc = [k for k, v in cn.items() if v == 1]
        if len(cc) == 3:
            cnt += len(cc) - 1
        else:
            cnt += len(cc)

    return cnt

def main():
    input = sys.stdin.readline
    n = int(input())
    a = input()
    b = input()
    c = input()

    print(r(n, a, b, c))


if __name__ == '__main__':
    main()