#include<iostream>
using namespace std;
int main()
{
	
	int n;
	string a,b,c;
	cin>>n;
	cin>>a>>b>>c;
	int cnt=0;
	for(int i=0;i<n;i++)
	{
		if(a[i]==b[i] && b[i]==c[i]) ;
		else if(a[i]==b[i] || b[i]==c[i] || c[i]==a[i]) cnt++;
		else cnt+=2;
	}
	cout<<cnt<<'\n';
	
	return 0;
}