ARC 119

void solve() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int N;
    cin >> N;
    string S, T;
    cin >> S >> T;

    vint s, t;
    rep(i, N) {
        if (S[i] == '0')
            s.push_back(i);
        if (T[i] == '0')
            t.push_back(i);
    }

    if (s.size() != t.size()) {
        cout << -1 << endl;
        return;
    }

    int ans = 0;
    rep(i, s.size()) {
        if (s[i] != t[i])
            ans++;
    }
    cout << ans << endl;
}