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