#include <iostream>
#include <string>
#include <vector>
#include <cmath>
using namespace std;

int n;
string s;
string t;
int a[200000];
int b[200000];

int main() {
	int i;
	
	cin >> n >> s >> t;
	if (s[0] != t[0] || s[n - 1] != t[n - 1]) {
		cout << -1 << endl;
		return 0;
	}
	
	vector<int> oneA;
	vector<int> oneB;
	for (i = 0; i < n - 1; i++) {
		a[i] = (s[i + 1] != s[i]);
		b[i] = (t[i + 1] != t[i]);
		if (i % 2 == 1) {
			a[i] = !a[i];
			b[i] = !b[i];
		}
		if (a[i]) oneA.push_back(i);
		if (b[i]) oneB.push_back(i);
	}
	if (oneA.size() != oneB.size()) {
		cout << -1 << endl;
		return 0;
	}
	
	int hanten = 0;
	for (i = 0; i < oneA.size(); i++) {
		hanten += abs(oneB[i] - oneA[i]);
	}
	
	cout << hanten << endl;
	return 0;
}