#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0; i<n; i++)
#define per(i,n) for(int i=(n)-1; i>=0; i--)
#define all(x) (x).begin(), (x).end()
bool chmax(auto& a, auto b) { return a<b ? a=b, 1: 0; }
bool chmin(auto& a, auto b) { return a>b ? a=b, 1: 0; }
using ll=long long; const int INF=1e9+10; const ll INFL=4e18;

#ifdef DEBUG
#include "./debug.hpp"
#else
#define debug(...)
#define print_line
#endif

//------>8------------------------------------------->8------

void run() {
    int N; cin>>N;
    string S,T; cin>>S>>T;

    if(S[0]!=T[0] || S[N-1]!=T[N-1]) {
        cout<<-1<<endl;
        return;
    }

    vector<int> ones,onet;
    rep(i,N-1) {
        int ds=(S[i]==S[i+1]);
        int dt=(T[i]==T[i+1]);
        if(i%2) {
            ds^=1;
            dt^=1;
        }
        if(ds) ones.push_back(i);
        if(dt) onet.push_back(i);
    }

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

    ll ans=0;
    rep(i,ones.size()) ans+=abs(ones[i]-onet[i]);
    cout<<ans<<endl;
}

int main() {
    ios::sync_with_stdio(false); cin.tie(nullptr);
    run();
}