import std.stdio, std.conv, std.string, std.bigint;
import std.math, std.random, std.datetime;
import std.array, std.range, std.algorithm, std.container, std.format;
string read(){ static string[] ss; while(!ss.length) ss = readln.chomp.split; string res = ss[0]; ss.popFront; return res; }

void main(){
	long n = read.to!long;
	string a = readln.chomp;
	string b = readln.chomp;
	string c = readln.chomp;
	
	long ans;
	foreach(i; 0 .. n){
		char x = a[i], y = b[i], z = c[i];
		if(x == y && y == z) ans += 0;
		else if(x == y || y == z || z == x) ans += 1;
		else ans += 2;
	}
	
	ans.writeln;
	
}
