#include "bits/stdc++.h"
using namespace std;
 
/* 
find my code templates at https://github.com/galencolin/cp-templates
also maybe subscribe please thanks 
*/
 
#define send {ios_base::sync_with_stdio(false);}
#define help {cin.tie(NULL);}
#define f first
#define s second
#define getunique(v) {sort(v.begin(), v.end()); v.erase(unique(v.begin(), v.end()), v.end());}
 
typedef long long ll;
// typedef int ll;
// #pragma warning("int")
 
typedef long double lld;
typedef unsigned long long ull;
 
template<typename A> ostream& operator<<(ostream &cout, vector<A> const &v);
template<typename A, typename B> ostream& operator<<(ostream &cout, pair<A, B> const &p) { return cout << "(" << p.f << ", " << p.s << ")"; }
template<typename A> ostream& operator<<(ostream &cout, vector<A> const &v) {
	cout << "["; for(int i = 0; i < v.size(); i++) {if (i) cout << ", "; cout << v[i];} return cout << "]";
}
template<typename A, typename B> istream& operator>>(istream& cin, pair<A, B> &p) {
	cin >> p.first;
	return cin >> p.second;
}
 
mt19937_64 rng(std::chrono::steady_clock::now().time_since_epoch().count());
// mt19937_64 rng(61378913);
/* usage - just do rng() */
 
void usaco(string filename) {
  // #pragma message("be careful, freopen may be wrong")
	freopen((filename + ".in").c_str(), "r", stdin);
	freopen((filename + ".out").c_str(), "w", stdout);
}
 
// #include <atcoder/all>
// using namespace atcoder;
 
const lld pi = 3.14159265358979323846;
// const ll mod = 1000000007;
// const ll mod = 998244353;
// ll mod;
 

 
ll n, m, q, k, l, r, x, y, z;
const ll template_array_size = 1e6 + 15258;
ll a[template_array_size];
ll b[template_array_size];
ll c[template_array_size];
string s, t;



void solve(int tc = 0) {
	cin >> n >> s >> t;
	string a = s, b = t;
	sort(a.begin(), a.end());
	sort(b.begin(), b.end());
	if (a != b) {
		cout << "-1\n";
		return;
	}
	
	vector<ll> at;
	for (ll i = 0; i < n; i++) if (t[i] == '0') at.push_back(i);
	
	ll ans = 0, pt = 0;
	for (ll i = 0; i < n; i++) {
		if (s[i] == '0') {
			if (i != at[pt++]) ++ans;
		}
	}
	cout << ans << '\n';
}
 
int main() {
	#ifdef galen_colin_local
		auto begin = std::chrono::high_resolution_clock::now();
	#endif
	
	send help
 
	#ifndef galen_colin_local
		// usaco("code");
	#endif
	
	// usaco("cowland");
	
	// freopen("tc.cpp", "r", stdin);
	// freopen("tc2.cpp", "w", stdout);
		
	cout << setprecision(15) << fixed;
		
	int tc = 1;
	// cin >> tc;
	for (int t = 0; t < tc; t++) solve(t);
	
	#ifdef galen_colin_local
		auto end = std::chrono::high_resolution_clock::now();
		cerr << setprecision(4) << fixed;
		cerr << "Execution time: " << std::chrono::duration_cast<std::chrono::duration<double>>(end - begin).count() << " seconds" << endl;
	#endif
}
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
#define FOR(i, a, b) for (int i = a; i < b; ++i)
#define REP(i, n) for (int i = 0; i < n; ++i)

int main() {
  string s, t;
  int n;
  cin >> n;
  cin >> s >> t;
  vector<int> szero;
  vector<int> tzero;
  REP(i, n) {
    if (s[i] - '0' == 0) {
      szero.push_back(i);
    }
    if (t[i] - '0' == 0) {
      tzero.push_back(i);
    }
  }

  if (szero.size() != tzero.size()) {
    cout << -1 << endl;
    return 0;
  }
  int length = szero.size();
  int ans = 0;
  REP(i, length) {
    if (szero[i] != tzero[i]) {
      ans++;
    }
  }
  cout << ans << endl;
  return 0;
}
