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 Perl (v5.18.2) (judge verdict: Accepted)

#!/usr/bin/perl
my ($n) = map { $_ - 0 } split(/\s+/,<STDIN>);
( my $a = <STDIN> ) =~ s/[\x0a\x0d]+$//ios;
( my $b = <STDIN> ) =~ s/[\x0a\x0d]+$//ios;
( my $c = <STDIN> ) =~ s/[\x0a\x0d]+$//ios;

my $tot = 0;
for(my $i=0;$i<$n;$i++){
  my $x = substr($a,$i,1);
  my $y = substr($b,$i,1);
  my $z = substr($c,$i,1);
  if( $x eq $y and $x eq $z ){
    $tot += 0;
  } elsif ( $x eq $y or $y eq $z or $z eq $x ){
    $tot += 1;
  } else {
    $tot += 2;
  }
}
print "$tot\n";