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

//#pragma GCC optimize("Ofast")
//#pragma GCC optimize ("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

#define FastIO()            ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define read()              freopen("in.txt","r",stdin)
#define write()             freopen("out.txt","w",stdout)

typedef long long           ll;
typedef unsigned long long  ull;
typedef double              dbl;
typedef float               flt;

typedef pair<int, int>      pii;
typedef pair<ll, ll>        pl;

typedef vector<int>         vi;
typedef vector<ll>          vl;
typedef vector<pii>         vpii;
typedef vector<pl>          vpl;

#define pie                 acos(-1)

#define mp                  make_pair
#define pb                  push_back
#define eb                  emplace_back
#define ff                  first
#define ss                  second

#define MAX                 300005
#define MOD                 1000000007
#define INF                 1000000100

#define for0(i, n)          for(ll i=0; i<n; i++)
#define for1(i, n)          for(ll i=1; i<=n; i++)
#define forab(i, a, b)      for(ll i=a; i<=b; i++)
#define forabx(i, a, b, x)  for(ll i=a; i<=b; i+=x)
#define forinv(i, a, b)     for(ll i=a; i>=b; i--)

#define clr0(a)             memset(a, 0, sizeof(a))
#define ceil(x, y)          (x+y-1) / (y)
#define max3(a, b, c)       max(a, max(b, c))
#define min3(a, b, c)       min(a, min(b, c))
#define gcd(a, b)           __gcd(a, b)
#define lcm(a, b)           ((a * b) / __gcd(a, b))
#define sort1(a, x, y)      sort(a+x, a+y+1)
#define debug(x)            cout << "DEBUG " << x << endl;

#define Y()                 cout << "YES" << endl;
#define N()                 cout << "NO" << endl;
#define inArr(a, x, y)      forab(i, x, y) { cin >> a[i]; }
#define outArr(a, x, y)     forab(i, x, y) { cout << a[i] << " "; } cout << endl;


void solve() {
    ll n;
    cin >> n;
    char a[n+10], b[n+10];
    cin >> a;
    cin >> b;
    vl a0, b0;
    ll ca=0, cb=0;
    for0(i, n) {
        if (a[i]=='0') {
            ca ++;
            a0.pb(i);
        }
        if (b[i]=='0') {
            cb++;
            b0.pb(i);
        }
    }
    ll ans = 0;
    if (ca!=cb) {
        ans = -1;
    }
    else {
        for0(i, ca) {
            if (a0[i]!=b0[i]) {
                ans ++;
            }
        }
    }
    cout << ans << endl;
}

void testcase() {
    ll t;
    cin >> t;
    while (t--) {
        solve();
    }
}

int main () {
    FastIO()

    //testcase();
    solve();

    return 0;
}


#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

#pragma GCC target ("avx2")
#pragma GCC optimization ("O3")
#pragma GCC optimization ("unroll-loops")
#pragma comment(linker, "/stack:200000000")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
//turn on extra precision
//#pragma GCC target("fpmath=387")

using namespace std;
using namespace __gnu_pbds;

typedef long long ll;
typedef string str;
typedef pair <int,int> pii;
typedef pair <ll,ll> pll;
typedef vector <int> vi;
typedef vector <ll> vll;
typedef vector <pii> vpii;
typedef vector <pll> vpll;

#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
#define ordered_multiset tree<int, null_type,less_equal<int>, rb_tree_tag,tree_order_statistics_node_update>
#define mp make_pair
#define pb push_back
#define pob pop_back
#define pf push_front
#define pof pop_front
#define fi first
#define se second
#define fs first.second
#define ss second.second
#define ff first.first
#define sf second.first
#define newl '\n'
#define fbo find_by_order
#define ook order_of_key
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(),x.rend()
#define watch(x) cout << (#x) << " is : " << (x) << newl

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
vi dirx = {0,0,1,-1};
vi diry = {1,-1,0,0};
char to_upper (char x){
    if( 97 <= int(x) && int(x) <= 122) return char(x-32);
    if( 65 <= int(x) && int(x) <= 90) return x;
    return -1;
}
char to_lower (char x){
    if( 97 <= int(x) && int(x) <= 122) return x;
    if( 65 <= int(x) && int(x) <= 90) return char(x+32);
    return -1;
}
int numerize (char x){
    if(48 <= int(x) && int(x) <= 57) return int(x-'0');
    if(97 <= int(x) && int(x) <= 122) return int(x-96);
    if(65 <= int(x) && int(x) <= 90) return int(x-64);
    return -1;
}
bool isect (int l1, int r1, int l2, int r2){ return max(l1,l2) <= min(r1,r2); }
ll quickpow (ll num1, ll num2, ll MOD){
    if(num2==0)return 1%MOD;
    else if(num2==1)return num1%MOD;
    else{
        ll temp = quickpow (num1,num2>>1LL,MOD); ll res = ((temp%MOD) * (temp%MOD))%MOD;
        if(num2&1) res = ((res%MOD)*(num1%MOD))%MOD; return res;
    }
}
ll invmod (ll num, ll MOD){return quickpow (num,MOD-2,MOD);}
ll gcd (ll num1, ll num2){
    if(num1 < num2) swap(num1,num2); ll num3 = num1 % num2 ;
    while(num3 > 0){ num1 = num2; num2 = num3; num3 = num1 % num2;}
    return num2;
}
ll lcm (ll num1 , ll num2){return (ll) (num1/__gcd(num1,num2))*num2;}
// end of Template

int main(){

//    freopen("input.txt", "r", stdin);
//    freopen("output.txt", "w", stdout);

    ios_base::sync_with_stdio(false);
    cin.tie(NULL);

    int a,b,c,d; cin >> a >> b >> c >> d;
    cout << b - c << newl;


    return 0;
}
