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++ (GCC 9.2.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
#define rep(i,x,n) for(int i=x; i<(int)(n); i++)
#define rep_eq(i,x,n) for(int i=x; i<=(int)(n); i++)
using namespace std;

using ll=long long;

using vi=vector<int>;
using vll=vector<ll>;
using vvi=vector<vi>;

int main() {
  int N; cin >>N;
  string A,B,C; cin >>A >>B >>C;
  int ans=0;
  rep(i,0,N) {
    set<char> a;
    a.insert(A[i]);
    a.insert(B[i]);
    a.insert(C[i]);
    ans+=a.size()-1;
  }
  cout <<ans <<endl;
  return 0;
}