#include <bits/stdc++.h>

using namespace std;

int main() {
	int n, r = 0;
	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])
			continue;
		if (a[i] == b[i] || a[i] == c[i] || b[i] == c[i])
			r++;
		else r += 2;
	}
	cout << r << endl;
	return 0;
}
