#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <array>
#include <atcoder/modint>

using namespace std;
using i32 = int32_t;
using u32 = uint32_t;
using i64 = int64_t;
using u64 = uint64_t;
#define rep(i,n) for(int i=0; i<(int)(n); i++)


const i64 INF = 1001001001001001001;
using modint = atcoder::static_modint<1000000007>;

int main(){
    int N; cin >> N;
    string S; cin >> S;
    vector<int> Sx(N-1);
    rep(i,N-1) Sx[i] = (S[i] == S[i+1]) ? 0 : 1;
    string T; cin >> T;
    vector<int> Tx(N-1);
    rep(i,N-1) Tx[i] = (T[i] == T[i+1]) ? 0 : 1;
    if(S[0] != T[0]){ cout << "-1n"; return 0; }

    N--;
    rep(i,N) if(i%2==0) Sx[i] ^= 1;
    rep(i,N) if(i%2==0) Tx[i] ^= 1;

    vector<int> Si;
    rep(i,N) if(Sx[i] == 0) Si.push_back(i);
    vector<int> Ti;
    rep(i,N) if(Tx[i] == 0) Ti.push_back(i);
    if(Si.size() != Ti.size()){ cout << "-1\n"; return 0; }

    i64 ans = 0;
    rep(i,Si.size()) ans += abs(Si[i] - Ti[i]);
    cout << ans << '\n';
    return 0;
}


struct ios_do_not_sync{
    ios_do_not_sync(){
        std::ios::sync_with_stdio(false);
        std::cin.tie(nullptr);
    }
} ios_do_not_sync_instance;