# include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
const double pi = acos(-1);
template<class T>constexpr T inf() { return ::std::numeric_limits<T>::max(); }
template<class T>constexpr T hinf() { return inf<T>() / 2; }
template <typename T_char>T_char TL(T_char cX) { return tolower(cX); }
template <typename T_char>T_char TU(T_char cX) { return toupper(cX); }
template<class T> bool chmin(T& a,T b) { if(a > b){a = b; return true;} return false; }
template<class T> bool chmax(T& a,T b) { if(a < b){a = b; return true;} return false; }
template<class T> bool is_sqare(T a) { if(floor(sqrt(a)) * floor(sqrt(a)) == a){ return true; }return false; }
int popcnt(unsigned long long n) { int cnt = 0; for (int i = 0; i < 64; i++)if ((n >> i) & 1)cnt++; return cnt; }
int d_sum(ll n) { int ret = 0; while (n > 0) { ret += n % 10; n /= 10; }return ret; }
int d_cnt(ll n) { int ret = 0; while (n > 0) { ret++; n /= 10; }return ret; }
ll gcd(ll a, ll b) { if (b == 0)return a; return gcd(b, a%b); };
ll lcm(ll a, ll b) { ll g = gcd(a, b); return a / g*b; };
template<class T> using dijk = priority_queue<T, vector<T>, greater<T>>;
# define all(qpqpq)           (qpqpq).begin(),(qpqpq).end()
# define UNIQUE(wpwpw)        (wpwpw).erase(unique(all((wpwpw))),(wpwpw).end())
# define LOWER(epepe)         transform(all((epepe)),(epepe).begin(),TL<char>)
# define UPPER(rprpr)         transform(all((rprpr)),(rprpr).begin(),TU<char>)
# define rep(i,upupu)         for(ll i = 0, i##_len = (upupu);(i) < (i##_len);(i)++)
# define reps(i,opopo)        for(ll i = 1, i##_len = (opopo);(i) <= (i##_len);(i)++)
# define len(x)                ((ll)(x).size())
# define bit(n)               (1LL << (n))
# define pb push_back
# define exists(c, e)         ((c).find(e) != (c).end())
#ifdef LOCAL
#  include "_debug_print.hpp"
#  define debug(...) debug_print::multi_print(#__VA_ARGS__, __VA_ARGS__)
#else
#  define debug(...) (static_cast<void>(0))
#endif

struct INIT{
	INIT(){
		std::ios::sync_with_stdio(false);
		std::cin.tie(0);
		cout << fixed << setprecision(20);
	}
}INIT;

void solve(){
	int n;
	cin >> n;
	vector<int> x(n), y(n);
	rep(i, n)cin >> x[i] >> y[i];
	set<pair<int, int>> cand_yx;
	int dx[] = {1, 2, 2, 1, -1, -2, -2, -1};
	int dy[] = {-2, -1, 1, 2, 2, 1, -1, -2};
	rep(i, n){
		rep(dir, 8){
			int ny = y[i] + dy[dir];
			int nx = x[i] + dx[dir];
			bool flg = true;
			rep(j, n)if(ny == y[j] && nx == x[j])flg = false;
			if(not flg)continue;
			cand_yx.insert({ny, nx});
		}
	}
	vector<int> dp(bit(n), hinf<int>());
	dp[0] = 0;
	for(auto [sy, sx] : cand_yx){
		auto ndp = dp;
		rep(subset, bit(n)){
			int dx2[] = {2, 2, -2, -2, -1, 1, -1, 1};
			int dy2[] = {-1, 1, -1, 1, -2, -2, 2, 2};
			rep(dir, 4){
				int ns = subset;
				rep(i, n){
					if(sy + dy2[2*dir + 0] == y[i] && sx + dx2[2*dir + 0] == x[i])ns |= bit(i);
					if(sy + dy2[2*dir + 1] == y[i] && sx + dx2[2*dir + 1] == x[i])ns |= bit(i);
				}
				chmin(ndp[ns], dp[subset]+1);
			}
		}
		dp = ndp;
	}
	if(dp[bit(n)-1] == hinf<int>()){
		cout << -1 << endl;
		return;
	}
	cout << dp[bit(n)-1] << endl;
}

int main(){
    int t = 1;
    //cin >> t;
    while(t--)solve();
}