#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; using ll = long long; using ull = unsigned long long; #define rep(i, a, b) for(int i = a; i < b; i++) #define rrep(i, a, b) for(int i = b - 1; i >= a; i--) #define ALL(a) a.begin(), a.end() using pii = pair; using piii = pair; using pll = pair; using plll = pair; // #pragma GCC optimize("Ofast") // #define _GLIBCXX_DEBUG #define pcnt __builtin_popcount #define buli(x) __builtin_popcountll(x) #define pb push_back #define mp make_pair #define UNIQUE(v) v.erase( unique(v.begin(), v.end()), v.end() ); #define isSquare(x) (sqrt(x)*sqrt(x) == x) templateinline bool chmax(T &a, const T &b) {if(ainline bool chmin(T &a, const T &b) {if(a>b){a = b; return 1;} return 0; }; inline void in(void){return;} template void in(First& first, Rest&... rest){cin >> first;in(rest...);return;} inline void out(void){cout << "\n";return;} template void out(First first, Rest... rest){cout << first << " ";out(rest...);return;} const double EPS = 1e-9; const int mod = 1e9 + 7; // const int mod = 998244353; const int INF = 1e9; const long long INFLL = 1e18; void iosetup() { cin.tie(nullptr);ios::sync_with_stdio(false); cout << fixed << setprecision(10); cerr << fixed << setprecision(10); } template< typename T1, typename T2 > ostream &operator<<(ostream &os, const pair< T1, T2 >& p) { os << p.first << " " << p.second; return os; } template< typename T1, typename T2 > istream &operator>>(istream &is, pair< T1, T2 > &p) { is >> p.first >> p.second; return is; } template< typename T > ostream &operator<<(ostream &os, const vector< T > &v) { for(int i = 0; i < (int) v.size(); i++) { os << v[i] << (i + 1 != v.size() ? " " : ""); } return os; } template< typename T > istream &operator>>(istream &is, vector< T > &v) { for(T &in : v) is >> in; return is; } template vector make_vec(size_t a) {return vector(a); } template auto make_vec(size_t a, Ts... ts){ return vector(ts...))>(a, make_vec(ts...)); } template pair operator+(const pair &s, const pair& t){return pair(s.first+t.first, s.second+t.second);} template pair operator-(const pair &s, const pair& t){return pair(s.first-t.first, s.second-t.second);} template pair operator*(const pair &s, const S& t){return pair(s.first*t, s.second*t);} template void Exit(T first){cout << first << endl;exit(0); }; template< int mod > struct ModInt { unsigned x; ModInt() : x(0) {} ModInt(int64_t y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {} ModInt &operator+=(const ModInt &p) {if((x += p.x) >= mod) x -= mod;return *this;} ModInt &operator-=(const ModInt &p) {if((x += mod - p.x) >= mod) x -= mod;return *this;} ModInt &operator*=(const ModInt &p) {x = (int) (1LL * x * p.x % mod);return *this;} ModInt &operator/=(const ModInt &p) {*this *= p.inverse();return *this;} ModInt operator-() const { return ModInt(-x); } ModInt operator+(const ModInt &p) const { return ModInt(*this) += p; } ModInt operator-(const ModInt &p) const { return ModInt(*this) -= p; } ModInt operator*(const ModInt &p) const { return ModInt(*this) *= p; } ModInt operator/(const ModInt &p) const { return ModInt(*this) /= p; } bool operator==(const ModInt &p) const { return x == p.x; } bool operator!=(const ModInt &p) const { return x != p.x; } ModInt inverse() const {int a = x, b = mod, u = 1, v = 0, t; while(b > 0) { t = a / b; swap(a -= t * b, b); swap(u -= t * v, v); }return ModInt(u);} ModInt pow(int64_t n) const {ModInt ret(1), mul(x); while(n > 0) {if(n & 1) ret *= mul;mul *= mul;n >>= 1;}return ret;} friend ostream &operator<<(ostream &os, const ModInt &p) { return os << p.x;} friend istream &operator>>(istream &is, ModInt &a) { int64_t t; is >> t; a = ModInt< mod >(t); return (is); } static int get_mod() { return mod; } }; using modint = ModInt< mod >; const int dx[4] = {1, 0, -1, 0}; const int dy[4] = {0, 1, 0, -1}; const pii dxy[4] = {pii(1,0), pii(0, 1), pii(-1, 0), pii(0, -1)}; //----------------------- edit from here --------------------------------- int main(){ iosetup(); int n; cin >> n; vector T(n); cin >> T; vector D = {0, 2, 4,5,7,9,11}; vector ans; rep(i, 0, 12){ bool flag = true; rep(j, 0, n){ bool F = false; for(auto d: D){ if(T[j]== (i + d) % 12){ F = true; } } if(!F) flag = false; } if(flag) ans.push_back(i); } if(ans.size() != 1) cout << -1 << endl; else cout << ans[0] << endl; return 0; }