#include<iostream>
#include<cstdio>
#include<cstdlib>
using namespace std;
char a[200],b[220],c[200];
int n;
int main()
{
	scanf("%d%s%s%s",&n,a+1,b+1,c+1);
	int ans=0;
	for(int i=1;i<=n;i++)
	{
		if(a[i]==b[i]&&b[i]==c[i]) continue;
		if(a[i]==b[i]||a[i]==c[i]||b[i]==c[i]) ans++;
		else ans+=2;
	}
	cout<<ans<<endl;
}
