#include <bits/stdc++.h>
using namespace std;
mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
const int SZ = 2e5 + 4;
const double EPS = 1e-7;
const int mod = 998244353;
const int hashpow = 2;
const int inf = 2e9;
struct custom_hash {
  static uint64_t splitmix64(uint64_t x) {
    x += 0x9e3779b97f4a7c15;
    x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
    x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
    return x ^ (x >> 31);
  }
  size_t operator()(uint64_t x) const {
    static const uint64_t FIXED_RANDOM =
        chrono::steady_clock::now().time_since_epoch().count();
    return splitmix64(x + FIXED_RANDOM);
  }
};
int n;
string s, t;
inline void read() { cin >> n >> s >> t; }
inline void solve() {
  string tmp;
  int cnt = 0;
  for (int i = 0; i < n; ++i) {
    if (s[i] != t[i]) {
      tmp += s[i];
      cnt += s[i] - '0';
    }
  }
  if (cnt * 2 != tmp.size()) {
    cout << -1 << "\n";
    return;
  }
  int zero = 0, one = 0;
  for (char c : tmp) {
    if (c == '1') {
      if (zero) {
        --zero;
      }
      ++one;
    } else {
      if (one) {
        --one;
      }
      ++zero;
    }
  }
  cout << zero + one << "\n";
}
signed main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  read();
  solve();
  return 0;
}
