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

int main()
{
	int n;
	string a, b, c;
	cin >> n >> a >> b >> c;
	int ans = 0;
	for (int i = 0; i < n; i++)
	{
		set<char> st;
		st.emplace(a[i]);
		st.emplace(b[i]);
		st.emplace(c[i]);
		ans += st.size() - 1;
	}
	cout << ans << endl;
	return 0;
}