#include <bits/stdc++.h>
using namespace std;

#define REP(i,n) for(ll i=0;i<(ll)n;i++)
#define dump(x)  cerr << "Line " << __LINE__ << ": " <<  #x << " = " << (x) << "\n";
#define spa << " " <<
#define fi first
#define se second
#define ALL(a)  (a).begin(),(a).end()
#define ALLR(a)  (a).rbegin(),(a).rend()

using ld = long double;
using ll = long long;
using ull = unsigned long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using pdd = pair<ld, ld>;

template<typename T> using V = vector<T>;
template<typename T> using P = pair<T, T>;
template<typename T> vector<T> make_vec(size_t n, T a) { return vector<T>(n, a); }
template<typename... Ts> auto make_vec(size_t n, Ts... ts) { return vector<decltype(make_vec(ts...))>(n, make_vec(ts...)); }
template<class S, class T> ostream& operator << (ostream& os, const pair<S, T> v){os << "(" << v.first << ", " << v.second << ")"; return os;}
template<typename T> ostream& operator<<(ostream &os, const vector<T> &v) { for (auto &e : v) os << e << ' '; return os; }
template<class T> ostream& operator<<(ostream& os, const vector<vector<T>> &v){ for(auto &e : v){os << e << "\n";} return os;}
struct fast_ios { fast_ios(){ cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;

template <class T> void UNIQUE(vector<T> &x) {sort(ALL(x));x.erase(unique(ALL(x)), x.end());}
template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }
void fail() { cout << -1 << '\n'; exit(0); }
inline int popcount(const int x) { return __builtin_popcount(x); }
inline int popcount(const ll x) { return __builtin_popcountll(x); }
template<typename T> void debug(vector<vector<T>>&v,ll h,ll w){for(ll i=0;i<h;i++)
{cerr<<v[i][0];for(ll j=1;j<w;j++)cerr spa v[i][j];cerr<<"\n";}};
template<typename T> void debug(vector<T>&v,ll n){if(n!=0)cerr<<v[0];
for(ll i=1;i<n;i++)cerr spa v[i];
cerr<<"\n";};

const ll INF = (1ll<<62);
// const ld EPS   = 1e-10;
// const ld PI    = acos(-1.0);
const ll mod = (int)1e9 + 7;
//const ll mod = 998244353;

int main(){

    ll N;
    string S, T;
    cin >> N >> S >> T;

    ll cntS=0, cntT=0;
    REP(i, N) cntS += (S[i] == '1');
    REP(i, N) cntT += (T[i] == '1');

    if(cntS != cntT){
        cout << -1 << endl;
        return 0;
    }

    V<ll> posS, posT;
    REP(i, N) if(S[i] == '0') posS.push_back(i);
    REP(i, N) if(T[i] == '0') posT.push_back(i);

    ll sz = posS.size();

    ll res = 0;
    REP(i, sz){
        if(posS[i] != posT[i]) res++;
    }

    cout << res << endl;

    return 0;
}
#include<iostream>
#include<string>
#include<queue>
using namespace std;
typedef long long ll;
const int N = 5e5+10;
string s,t;
int sums = 0,sumt = 0,cnt;
bool st[N],flag = false;
priority_queue<int,vector<int>,greater<int>> fla;
int main()
{
	int n;
	scanf("%d",&n);
	cin>>s>>t;
	for(int i = 0;i<n;i++)
	{
		sums+=s[i]-'0';
		sumt+=t[i]-'0';
		if((sums != sumt || s[i] != t[i]) && s[i] == '0')cnt++;
	}
	if(sums != sumt)printf("-1\n");
	else printf("%d\n",cnt);
	return 0;
}
