#include <bits/stdc++.h>
using namespace std;

int main(){
	int n;
	cin>>n;
	string a, b, c;
	cin>>a>>b>>c;
	int ans = 0;
	for(int i=0; i<n; i++){
		if(a[i]==b[i] && b[i]==c[i]){
			continue;
		}
		if(a[i]==b[i]){
			ans++;
		}else if(a[i]==c[i]){
			ans++;
		}else if(b[i]==c[i]){
			ans++;
		}else{
			ans+=2;
		}
	}
	cout<<ans<<endl;
}