#include <bits/stdc++.h>
using namespace std;
int n,i,s;
string a,b,c;
set<char> aa; 
int main()
{
	cin>>n>>a>>b>>c;
	for (i=0;i<n;i++)
	{
		aa.clear();aa.insert(a[i]);aa.insert(b[i]);aa.insert(c[i]);s+=aa.size()-1;
	}
	cout<<s<<endl;
	return 0;
}