// #pragma GCC optimize ("Ofast")
// #pragma GCC optimize ("unroll-loops")
// #pragma GCC target ("avx,avx2,fma")
#include <bits/stdc++.h>

using std::cin, std::cout, std::cerr;
using ll = long long;

int main() {
    std::ios::sync_with_stdio(false);
    int n; cin >> n;
    std::string s, t;
    auto f = [&](std::string s) {
        std::vector<int> r;
        for(int i = 0; i + 1 < n; i ++) {
            int x = (s[i] - 'A') ^ (s[i + 1] - 'A');
            if(i % 2 == 0) x = 1 - x;
            r.push_back(x);
        }
        return r;
    };

    cin >> s;
    auto a = f(s);
    cin >> t;
    auto b = f(t);

    if(s[0] != t[0] || s.back() != t.back() || std::ranges::count(a, 1) != std::ranges::count(b, 1)) {
        cout << -1 << '\n';
    } else {
        int p = 0;
        ll ans = 0;
        for(int i = 0; i < a.size(); i ++) if(a[i] == 1) {
            while(b[p] != 1) p ++;
            ans += std::abs(i - p);
            p ++;
        }
        cout << ans << '\n';
    }
}