#include <bits/stdc++.h>
#include <iomanip>
using namespace std;
#define reps(i,s,n) for(int i = s; i < n; i++)
#define rep(i,n) reps(i,0,n)
#define Rreps(i,n,e) for(int i = n - 1; i >= e; --i)
#define Rrep(i,n) Rreps(i,n,0)
#define ALL(a) a.begin(), a.end()
#define fi first
#define se second
typedef long long ll;
typedef vector<ll> vec;
typedef vector<vec> mat;

ll N,M,H,W,Q,K,A,B;
string S;
const ll MOD = 998244353;
//const ll MOD = (1e+9) + 7;
typedef pair<ll, ll> P;
const ll INF = (1LL<<60);

int main() {
    cin>>N;
    set<ll> a;
    ll k = 0, last = -1, f;
    rep(i,N){
        cin>>A;
        a.insert(A);
        if(last != A) ++k;
        last = A;
        if(i == 0) f = A;
    }
    if(f != last || k == 1){
        cout<<(k == a.size() ? 0 : -1)<<endl;
    }else{
        cout<<(k - 1 == a.size() ? 1 : -1)<<endl;
    }
}