//include //------------------------------------------ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include using namespace std; // typedef //------------------------------------------ typedef long long LL; typedef vector VI; typedef vector VB; typedef vector VC; typedef vector VD; typedef vector VS; typedef vector VLL; typedef vector VVI; typedef vector VVB; typedef vector VVS; typedef vector VVLL; typedef vector VVVI; typedef vector VVVLL; typedef pair PII; typedef pair PLL; typedef pair PIS; typedef pair PSI; typedef pair PSS; typedef vector VPII; typedef vector VPLL; typedef vector VVPII; typedef vector VVPLL; typedef vector VVS; typedef map MII; typedef map MLL; typedef map MSI; typedef map MIS; // container util //------------------------------------------ #define ALL(a) (a).begin(),(a).end() #define SZ(a) int((a).size()) #define EACH(i, arr) for(typeof((arr).begin()) i=(arr).begin(); i!=(arr).end(); ++i) #define EXIST(str, e) ((str).find(e)!=(str).end()) #define COUNT(arr, v) count((arr).begin(), (arr).end(), v) #define SEARCH(v, w) search((v).begin(), (v).end(), (w).begin(), (w).end()) #define SORT(c) sort((c).begin(),(c).end()) #define RSORT(c) sort((c).rbegin(),(c).rend()) #define REVERSE(c) reverse((c).begin(), (c).end()) #define ROTATE_LEFT(arr, c) rotate((arr).begin(), (arr).begin()+(c), (arr).end()) #define ROTATE_RIGHT(arr, c) rotate((arr).rbegin(), (arr).rbegin() + (c), (arr).rend()) #define SUMI(arr) accumulate((arr).begin(), (arr).end(), 0) #define SUMD(arr) accumulate((arr).begin(), (arr).end(), 0.) #define SUMLL(arr) accumulate((arr).begin(), (arr).end(), 0LL) #define MULD(arr) accumulate((arr).begin(), (arr).end(), 1., multiplies()) #define UB(arr, n) upper_bound((arr).begin(), (arr).end(), n) #define LB(arr, n) lower_bound((arr).begin(), (arr).end(), n) #define PB push_back #define MP make_pair #define ft first #define sd second // input output //------------------------------------------ #define GL(s) getline(cin, (s)) #define INIT() std::ios::sync_with_stdio(false);std::cin.tie(0) #define OUT(d) std::cout<<(d) #define OUT_L(d) std::cout<<(d)< istream &operator>>(istream &in, pair &p) { in >> p.first >> p.second; return in; } template istream &operator>>(istream &in, vector &v) { for (auto &x: v) in >> x; return in; } template ostream &operator<<(ostream &out, const std::pair &p) { out << "[" << p.first << ", " << p.second << "]" << "\n"; return out; } template inline bool chmin(T1 &a, T2 b) { if (a > b) { a = b; return true; } return false; } template inline bool chmax(T1 &a, T2 b) { if (a < b) { a = b; return true; } return false; } //repetition //------------------------------------------ #define FOR(i, a, b) for(int i=(a);i<(b);++i) #define RFOR(i, a, b) for(int i=(b)-1;i>=(a);--i) #define REP(i, n) FOR(i,0,n) #define RREP(i, n) for(int i = n-1;i >= 0;i--) #define FORLL(i, a, b) for(LL i=LL(a);i=LL(a);--i) #define REPLL(i, n) for(LL i=0;i=0;--i) #define FOREACH(x, arr) for(auto &(x) : (arr)) // Option + Control + K Terminal // Command + Control + K Run // Command + b EOF //------------------------------------------ //------------------------------------------ int main() { int N; cin >> N; vector A(N); cin >> A; map mp; for (int i = 0, j = 0; i < N; i = j) { while (j < N and A[i] == A[j])j++; mp[A[i]]++; } int cnt = 0; for (auto x: mp) if (x.second >= 2) cnt++; if (cnt == 0) cout << 0 << endl; else if (cnt == 1 and A.back() == A.front()) cout << 1 << endl; else cout << -1 << endl; }