#include<bits/stdc++.h>
using namespace std;
int main()
{
	string a,b,c;
	int n;
	cin>>n>>a>>b>>c;
	int ans=0;
	for (int i=0;i<n;i++)
	{
		if (a[i]==b[i] && b[i]==c[i] && a[i]==c[i]) ans+=0;
		else if (a[i]!=b[i] && b[i]!=c[i] && a[i]!=c[i])ans+=2;
		else ans++;
	}
	cout<<ans;
	return 0;
} 