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

int main()
{
	int n;
	cin >> n;
	char a[n] ,b[n], c[n];
	cin >> a >> b >> c;

	int ans = 0;
	for(int i = 0; i < n; i++){
		if(a[i] != b[i] && b[i] != c[i] && c[i] != a[i]){
			ans += 2;
		}else if(a[i] == b[i] && b[i] == c[i]){
		}else{
			ans++;
		}
	}

	cout << ans << "\n";

	return 0;
}
