#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main(){
    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 0;
    }
    vector<int> s = {}, t = {};
    for(int i=0;i<N-1;i++){
    	if((S[i] != S[i+1])^(i&1)) s.push_back(i);
    	if((T[i] != T[i+1])^(i&1)) t.push_back(i);
    }
    if(s.size() != t.size()) cout<<-1<<endl;
    else{
    	int ans = 0;
    	for(int i=0;i<s.size();i++) ans += abs(s[i]-t[i]);
    	cout<<ans<<endl;
    }
}