#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
#define REP(i, n) for (int i = 0; i < (n); ++i)
#define REPR(i, n) for (int i = n - 1; i >= 0; --i)
#define FOR(i, m, n) for (int i = m; i < n; ++i)
#define FORR(i, m, n) for (int i = m; i >= n; --i)
#define ALL(v) (v).begin(),(v).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 (b<a) { a=b; return 1; } return 0; }
const ll INF=1LL<<60;
const int inf=(1<<30)-1;
const int mod=1e9+7;
int dx[8]={1,0,-1,0,-1,-1,1,1};
int dy[8]={0,1,0,-1,-1,1,-1,1};
int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n;cin >> n;
    string s,t;cin >> s >> t;
    int cnt=0;
    REP(i,n) cnt+=s[i]-'0';
    REP(i,n) cnt-=t[i]-'0';
    if(cnt!=0){
        cout << -1 << endl;
        return 0;
    }
    vector<int> a,b;
    REP(i,n){
        if(s[i]=='0') a.push_back(i);
        if(t[i]=='0') b.push_back(i);
    }
    int ans=0;
    REP(i,a.size()) if(a[i]!=b[i]) ans++;
    cout << ans << endl;
}
#include<iostream>
#include<vector>
using namespace std;
const int N=1e6+7;
int n,a[N],b[N],sa,sb;
vector<int>ho,aq;
int main(){
	scanf("%d",&n);
	for(int i=1;i<=n;i++){
		scanf("%1d",&a[i]);
		sa+=a[i];
		if(!a[i])ho.push_back(i);
	}
	for(int i=1;i<=n;i++){
		scanf("%1d",&b[i]);
		sb+=b[i];
		if(!b[i])aq.push_back(i);
	}
	if(sa!=sb){
		puts("-1");
		return 0;
	}
	int ans=0;
	for(int i=0;i<ho.size();i++){
		if(ho[i]!=aq[i])ans++;
	}
	printf("%d\n",ans);
}