#pragma GCC optimize ("O3")
#pragma GCC target ("avx2")
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for(int i = 0; i < (n); i++)
#define rep1(i, n) for(int i = 1; i <= (n); i++)
#define co(x) cout << (x) << "\n"
#define cosp(x) cout << (x) << " "
#define ce(x) cerr << (x) << "\n"
#define cesp(x) cerr << (x) << " "
#define pb push_back
#define mp make_pair
#define chmin(x, y) x = min(x, y)
#define chmax(x, y) x = max(x, y)
#define Would
#define you
#define please


int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);


	int N;
	cin >> N;
	int A[100000];
	rep(i, N) cin >> A[i];

	int B[100001] = {};
	int dame = 0;
	int mae = -1;
	rep(i, N) {
		if (mae != A[i]) {
			if (B[A[i]]) dame++;
			B[A[i]]++;
			mae = A[i];
		}
	}

	if (dame == 0) {
		co(0);
		return 0;
	}
	if (A[0] == A[N - 1] && B[A[0]] == 2 && dame == 1) {
		dame = 0;
	}
	if (dame) co(-1);
	else co(1);

	Would you please return 0;
}