#include <bits/stdc++.h>
#define db1(x) cout<<#x<<"="<<x<<'\n'
#define db2(x,y) cout<<#x<<"="<<x<<","<<#y<<"="<<y<<'\n'
#define db3(x,y,z) cout<<#x<<"="<<x<<","<<#y<<"="<<y<<","<<#z<<"="<<z<<'\n'
#define rep(i,n) for(int i=0;i<(n);++i)
#define repA(i,a,n) for(int i=a;i<=(n);++i)
#define fast ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
 
#define repD(i,a,n) for(int i=a;i>=(n);--i)
 
using namespace std;
using ll =   long long;
ll dp[5005][5005];
ll fact(ll n)
{
    if(n==0||n==1)return 1;
    else {
        ll ans = n;
        n--;
        while(n!=1)
        {
            ans *= n;
            n--;
        }
        return ans;
    }
}
set<ll> taken;
ll m;
ll a[5005];
//vector <ll> ones, zeros;
// ll solve(ll i, ll start, ll n)
// {
//     if(i==m)return 0;
//     else {
//         if(dp[i][start]!=-1)return dp[i][start];
//         //a[ones[i]] = 0;
//         ll ans = 100000000000;
//         //a[ones[i]] = 0;
//         ans = min( ans, solve(i+1,start + 1,vis1, vis2,n) + abs(ones[i]-start));
//         ans = min(ans, solve(i+1, start))
        
//         return dp[i][start] = ans;
//     }
// }
int main()
{
    ll n;
    cin>>n;
    //ll a[n];
    ll i,j;
    string s,t;
    cin>>s>>t;
    set <ll,greater<>> szero,tzero;
    for(i=0;i<n;i++)
    {
        if(s[i]=='0')
        {
            szero.insert(i);
        }
        if(t[i]=='0')
        {
            tzero.insert(i);
        }
    }
    if (tzero.size()!=szero.size()) {
      cout << -1;
      return 0;
   }
    ll f = 0;
    ll ans = 0;
    for(auto it: tzero)
    {
        if(it!=*szero.begin())
        {
            ans++;
        }
        szero.erase(szero.begin());
        
    }
    if(f)ans = -1;
        cout<<ans<<endl;
}
#include <bits/stdc++.h>
 
using namespace std;
 
typedef long long ll;
typedef long double ld;
 
typedef vector<int> vi;
typedef vector<ll> vll;
 
typedef vector<vi> vvi;
typedef vector<vll> vvll;
 
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
 
typedef vector<pii> vpii;
typedef vector<pll> vpll;
 
typedef vector<vpii> vvpii;
typedef vector<vpll> vvpll;
 
#define pb push_back
#define mp make_pair
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) (int)(x).size()
#define fi first
#define se second
 
template<class T> bool ckmin(T &a, const T &b) {return a > b ? a = b, 1 : 0;}
template<class T> bool ckmax(T &a, const T &b) {return a < b ? a = b, 1 : 0;}
 
void __print(int x) {cerr << x;}
void __print(long long x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}
 
template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ','; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for(auto z : x) cerr << (f++ ? "," : ""), __print(z); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if(sizeof...(v)) cerr << ", "; _print(v...);}
 
#ifdef ljuba
#define dbg(x...) cerr << "LINE(" << __LINE__ << ") -> " << "[" << #x << "] = ["; _print(x)
#else
#define dbg(x...)
#endif
 
const char nl = '\n';
 
void solve() {
    int n;
    cin >> n;
    vi v(n);
    for(auto &z : v)
        cin >> z;
    int mini = *min_element(all(v));

    map<int, int> ma;

    for(auto z : v) {
        for(int i = 1; i * i <= z; ++i) {
            if(z % i == 0) {
                ma[i] = __gcd(ma[i], z);
                if(z / i != i)
                    ma[z/i] = __gcd(ma[z/i], z);
            }
        }
    }

    dbg(ma);

    int ans = 0;
    for(auto z : ma) {
        if(z.fi == z.se && z.fi <= mini)
            ++ans;
    }

    cout << ans << nl;
}
 
int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
 
    int testCases = 1;
    //cin >> testCases;
    while(testCases--)
        solve();
 
}
