#include <bits/stdc++.h>
using namespace std;
char a[101],b[101],c[101];
int main()
{
	int n,i,ans=0;
	scanf("%d",&n);
	scanf("%s",a);
	scanf("%s",b);
	scanf("%s",c);
	for(i=0;i<n;i++)
	{
		if(a[i]!=b[i]&&a[i]!=c[i]&&b[i]!=c[i])
			ans+=2;
		else if(a[i]==b[i]&&b[i]==c[i])
			ans+=0;
		else
			ans+=1;
	}
	printf("%d",ans);
	return 0;
}