#include <iostream>
#include <string>
using namespace std;
int main() {
	int n;
	int ans = 0;
	string S, T;
	cin >> n >> S >> T;
	if (S == T) {
		cout << ans << endl; return 0;
	}
	else {
		for (int i = 0; i < n;i++) {
			if (S[i] != T[i]) {
				S[i] = T[i];
				ans++;
				if (S == T) {
					break;
				}
			}
		}
	}
	cout << ans << endl;
	return 0;
}