#include<bits/stdc++.h>
using namespace std;
double PI=acos(-1.0);
#define ll long long
#define pii pair<ll,ll>
const ll mod=998244353;
int a[500007];
int b[500007];
int main()
{
    ios::sync_with_stdio(0);
    int n;
    cin>>n;
    string s1,s2;
    cin>>s1>>s2;
    ll ans=0,ans1=0;
    int num1=0,num2=0;
    for(int i=0;i<n;i++)
    {
        if(s1[i]=='0')
        {
            a[num1++]=i;
            ans++;
        }
        if(s2[i]=='0')
        {
            b[num2++]=i;
            ans1++;
        }
    }
    if(ans!=ans1)
    {
        printf("-1\n");
    }
    else
    {
        ll sum=0;
        for(int i=0;i<ans;i++)
        {
            if(a[i]>b[i])
            {
                a[i]=b[i];
                sum++;
            }
        }
        for(int i=ans-1;i>=0;i--)
        {
            if(a[i]<b[i])
            {
                a[i]=b[i];
                sum++;
            }
        }
        cout<<sum<<endl;
    }
    return 0;
}
//#include <bits/stdc++.h>
#include <iostream> // cout, endl, cin
#include <string> // string, to_string, stoi
#include <vector> // vector
#include <algorithm> // min, max, swap, sort, reverse, lower_bound, upper_bound
#include <utility> // pair, make_pair
#include <tuple> // tuple, make_tuple
#include <cstdint> // int64_t, int*_t
#include <cstdio> // printf
#include <map> // map
#include <queue> // queue, priority_queue
#include <set> // set
#include <stack> // stack
#include <deque> // deque
#include <unordered_map> // unordered_map
#include <unordered_set> // unordered_set
#include <bitset> // bitset
#include <cctype> // isupper, islower, isdigit, toupper, tolower
#include <iomanip>
#include <math.h>

using namespace std;

#define rep(i,n) for(int i = 0; i < (n); i++)
#define pb push_back 
#define eb emplace_back 
#define all(x) x.begin() , x.end()
#define fi frist
#define se second
#define Yes() {puts("YES");return;}
#define No()  {puts("No"); return;}
#define P pair <int , int>
#define vi vector<int> 
#define vvi vector<<vector<int>> 
#define vs vector<string> 

typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;

const int INF = 1001001001;
const int mod = 1000000007;
const ld PI = 3.14159265358979;

ll gcd (ll a , ll b) {
    if (a < b) swap(a , b);
    if (b == 0) return 1;
    if (a % b == 0) return b;
    else return gcd (b , a % b);
}

bool is_prime (ll x) {
	if (x == 1) {
		return false;
	}
	if (x == 2 || x == 3 || x == 5 || x == 7) {
		return true;
	}
	if((x & 1) == 0){
		return false;
	}
	for (ll i = 3; i * i <= x; i += 2) {
		if(x % i == 0)return false;
	}
	return true;
}

bool is_2power(ll x) {
	if((x & (x - 1)) == 0) {
	    return true;
	} else {
	    return false;
	}
}

vector<int> divisor (ll x) {
	vector<int> ret;
	for (int i = 2; i * i <= x; i++) {
		while (x % i == 0) {
			ret.push_back(i);
			x /= i;
		}
	}
	if (x > 1) {
		ret.push_back(x);
	}
	return ret;
}

ll modpow (ll x , ll p , ll m) {
	ll ret = 1;
	while (p > 0) {
		if(p & 1)ret *= x;
		x *= x;
		x %= m;
		p >>= 1;
	}
	return ret;
}

int main(void){
    cin.tie(0);
	ios::sync_with_stdio(false);
    //cout << fixed << setprecision(15);
    int n;
    cin >> n;
    vi a(n) , p(n) , x(n);
    rep(i,n)cin >> a[i] >> p[i] >> x[i];
    int ans = INF;
    rep(i,n){
        if(x[i] - a[i] >= 1){
            ans = min(ans , p[i]);
        }
    }
    if(ans == INF)ans = -1;
    cout << ans << endl;
    return 0;
}
