#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int n;
    cin >> n;
    string s, t;
    cin >> s >> t;
    if (s[0] != t[0]) {
        cout << -1 << endl;
        return 0;
    }
    vector<ll> a, b;
    for (int i = 0; i + 1 < n; ++i) {
        int diff = abs(s[i] - s[i + 1]);
        if (i % 2) diff ^= 1;
        if (diff) a.push_back(i);
    }
    for (int i = 0; i + 1 < n; ++i) {
        int diff = abs(t[i] - t[i + 1]);
        if (i % 2) diff ^= 1;
        if (diff) b.push_back(i);
    }
    if (a.size() != b.size()) {
        cout << -1 << endl;
        return 0;
    }
    ll res = 0;
    for (int i = 0; i < a.size(); ++i) {
        res += abs(a[i] - b[i]);
    }
    cout << res << endl;
}