#include<iostream>
#include<string>
#include<algorithm>
#include<vector>
#include<queue>
#include<map>
#include<math.h>
#include<iomanip>
#include<set>
#include<numeric>
#include<cstring>
#include<cstdio>
#include<functional>
#include<bitset>
#include<limits.h>
#include<cassert>
#include<iterator>
#include<complex>
#include<stack>
#include<sstream>
#include<iterator>
#include<list>

using namespace std;

typedef  long long int lint;

#define rep(i, n) for (lint i = 0; i < n; i++)
#define sort(v) sort((v).begin(), (v).end())
#define reverse(v) reverse((v).begin(), (v).end())
#define upper(v,hoge) upper_bound(v.begin(),v.end(),hoge)
#define lower(v,hoge) lower_bound(v.begin(),v.end(),hoge)
#define mp make_pair
#define IP pair<int,int>
#define enld endl

int main() {
	lint N;
	cin >> N;
	vector<lint>A(N);
	rep(i, N) {
		cin >> A[i];
	}
	vector<lint>B;
	rep(i, N) {
		if (i == 0) {
			B.push_back(A[i]);
		}
		else {
			if (B.back() == A[i]) {

			}
			else {
				B.push_back(A[i]);
			}
		}
	}
	bool flag = true;
	if (B.back() == B.front()) {
		B.pop_back();
		flag = false;
	}
	set<lint>S;
	rep(i, B.size()) {
		S.insert(B[i]);
	}
	if (S.size() == B.size()) {
		if (flag == false) {
			cout << 1 << enld;
		}
		else {
			cout << 0 << enld;
		}
	}
	else {
		cout << -1 << enld;
	}
}