#include using namespace std; #define SZ(x) (int) (x).size() #define REP(i, n) for(int i = 0; i < (n); i++) #define FOR(i, a, b) for(auto i = (a); i < (b); i++) #define For(i, a, b, c) \ for(auto i = (a); i != (b); i += (c)) #define REPR(i, n) for(auto i = (n) -1; i >= 0; i--) #define ALL(s) (s).begin(), (s).end() #define so(V) sort(ALL(V)) #define rev(V) reverse(ALL(V)) #define uni(v) v.erase(unique(ALL(v)), (v).end()) #define eb emplace_back typedef unsigned long long ull; typedef long long ll; typedef vector vi; typedef vector vll; typedef vector vb; typedef vector vvi; typedef vector vvll; typedef pair PI; typedef pair PL; const double EPS = 1e-6; const int MOD = 1e9 + 7; const int INF = (1 << 30); const ll LINF = 1e18; const double math_PI = acos(-1); template vector make_v(size_t a) { return vector(a); } template auto make_v(size_t a, Ts... ts) { return vector(ts...))>( a, make_v(ts...)); } template typename enable_if::value == 0>::type fill_v( T& t, const V& v) { t = v; } template typename enable_if::value != 0>::type fill_v( T& t, const V& v) { for(auto& e: t) fill_v(e, v); } template bool chmax(T& a, const T& b) { if(a < b) { a = b; return true; } return false; } template bool chmin(T& a, const T& b) { if(a > b) { a = b; return true; } return false; } template istream& operator>>(istream& is, pair& p) { cin >> p.first >> p.second; return is; } template istream& operator>>(istream& is, vector& vec) { for(T& x: vec) is >> x; return is; } template string join(vector& vec, string splitter) { stringstream ss; REP(i, SZ(vec)) { if(i != 0) ss << splitter; ss << vec[i]; } return ss.str(); } template ostream& operator<<(ostream& os, vector& vec) { os << join(vec, " "); return os; } int main() { cin.tie(nullptr); ios::sync_with_stdio(false); int N; cin >> N; vector UMA(N); cin >> UMA; map M; REP(i, N) { M[UMA[i]] = i + 1; } set cand; vi dx { 2, 2, -2, -2, -1, 1, -1, 1 }; vi dy { -1, 1, -1, 1, -2, -2, 2, 2 }; REP(i, N) { REP(d, 8) { int ny = UMA[i].first + dy[d]; int nx = UMA[i].second + dx[d]; cand.emplace(ny, nx); } } auto dp = vi(1 << N, INF); dp[0] = 0; for(auto [y, x]: cand) { if(M.count({ y, x }) > 0) continue; REP(i, 1 << N) { if(dp[i] == INF) continue; REP(d, 4) { int nb = 0; int ny = y + dy[d * 2 + 1]; int nx = x + dx[d * 2 + 1]; if(M.count({ ny, nx }) > 0) { nb |= 1 << (M[{ ny, nx }] - 1); } ny = y + dy[d * 2]; nx = x + dx[d * 2]; if(M.count({ ny, nx }) > 0) { nb |= 1 << (M[{ ny, nx }] - 1); } chmin(dp[i | nb], dp[i] + 1); } } } if(dp[(1 << N) - 1] == INF) { cout << -1 << endl; } else { cout << dp[(1 << N) - 1] << endl; } return 0; }