#include <algorithm>
#include <iostream>
#include <numeric>
#include <string>
#include <tuple>
#include <utility>
#include <vector>
#include <limits>

#define rep(i, a, b) for (int i = int(a); i < int(b); i++)
using namespace std;
using ll = long long int;  // NOLINT
using P = pair<ll, ll>;

// clang-format off
#ifdef _DEBUG_
#define dump(...) do{ cerr << __LINE__ << ":\t" << #__VA_ARGS__ << " = "; debug_print(__VA_ARGS__); } while(false)
template<typename T, typename... Ts> void debug_print(const T &t, const Ts &...ts) { cerr << t; ((cerr << ", " << ts), ...); cerr << endl; }
#else
#define dump(...) do{ } while(false)
#endif
template<typename T> vector<T> make_v(size_t a, T b) { return vector<T>(a, b); }
template<typename... Ts> auto make_v(size_t a, Ts... ts) { return vector<decltype(make_v(ts...))>(a, make_v(ts...)); }
template<typename T> bool chmin(T &a, const T& b) { if (a > b) {a = b; return true; } return false; }
template<typename T> bool chmax(T &a, const T& b) { if (a < b) {a = b; return true; } return false; }
template<typename T, typename... Ts> void print(const T& t, const Ts&... ts) { cout << t; ((cout << ' ' << ts), ...); cout << '\n'; }
template<typename... Ts> void input(Ts&... ts) { (cin >> ... >> ts); }
template<typename T> istream &operator,(istream &in, T &t) { return in >> t; }
struct Inf { template<typename T> constexpr operator T() { return numeric_limits<T>::max() / 2; } };
// clang-format on

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int n;
    string s, t;
    cin, n, s, t;

    if (s.front() != t.front() || s.back() != t.back()) {
        print(-1);
        return 0;
    }

    vector<int> vs, vt;
    rep(i, 0, n - 1) {
        vs.emplace_back((s[i] ^ s[i + 1]) & 1);
        vt.emplace_back((t[i] ^ t[i + 1]) & 1);
    }
    rep(i, 0, n - 1) {
        vs[i] = vs[i] ^ (i & 1);
        vt[i] = vt[i] ^ (i & 1);
    }

    vector<int> zs, zt;
    rep(i, 0, n - 1) {
        if (vs[i]) zs.emplace_back(i);
        if (vt[i]) zt.emplace_back(i);
    }
    if (zs.size() != zt.size()) {
        print(-1);
        return 0;
    }

    ll ans = 0;
    rep(i, 0, zs.size()) {
        ans += abs(zs[i] - zt[i]);
    }

    print(ans);
    return 0;
}