#include <bits/stdc++.h>
#pragma GCC optimize("unroll-loops")
using namespace std;
using std::cout;
using std::cin;
using std::endl;
using ll=long long;
using ld=long double;
const ll ILL=2167167167167167167;
const int INF=2100000000;
const int mod=998244353;
#define rep(i,a,b) for (int i=(int)(a);i<(int)(b);i++)
#define all(p) p.begin(),p.end()
template<class T> using _pq = priority_queue<T, vector<T>, greater<T>>;
template<class T> ll LB(vector<T> &v,T a){return lower_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> ll UB(vector<T> &v,T a){return upper_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> bool chmin(T &a,T b){if(a>b){a=b;return 1;}else return 0;}
template<class T> bool chmax(T &a,T b){if(a<b){a=b;return 1;}else return 0;}
template<class T> void So(vector<T> &v) {sort(v.begin(),v.end());}
template<class T> void Sore(vector<T> &v) {sort(v.begin(),v.end(),[](T x,T y){return x>y;});}
void yneos(bool a,bool upp=0){if(a) cout<<(upp?"YES\n":"Yes\n"); else cout<<(upp?"NO\n":"No\n");}
template<class T> void vec_out(vector<T> &p,int ty=0){
if(ty==2){cout<<'{';for(int i=0;i<(int)p.size();i++){if(i){cout<<",";}cout<<'"'<<p[i]<<'"';}cout<<"}\n";}
else{if(ty==1){cout<<p.size()<<"\n";}for(int i=0;i<(int)(p.size());i++){if(i) cout<<" ";cout<<p[i];}cout<<"\n";}}
template<class T> T vec_min(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmin(ans,x);return ans;}
template<class T> T vec_max(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmax(ans,x);return ans;}
template<class T> T vec_sum(vector<T> &a){T ans=T(0);for(auto &x:a) ans+=x;return ans;}
int pop_count(long long a){int res=0;while(a){res+=(a&1),a>>=1;}return res;}



void solve();
// oddloop
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    int t=1;
    //cin>>t;
    rep(i,0,t) solve();
}

void solve(){
    int N;
    cin>>N;
    vector<int> X(N),Y(N);
    rep(i,0,N) cin>>X[i]>>Y[i];
    set<pair<int,int>> s;
    vector<int> dx={2,2,-2,-2,-1,1,-1,1};
    vector<int> dy={-1,1,-1,1,-2,-2,2,2};
    auto f=[&](int ind,int k=-1) -> pair<int,int> {
        if(k<0) return {X[ind],Y[ind]};
        return {X[ind]+dx[k],Y[ind]+dy[k]};
    };
    vector G(N,vector<vector<pair<int,int>>>(N));
    rep(i,0,N) rep(j,i+1,N){
        rep(k,0,8){
            if(f(i,k)==f(j,k^1)) G[i][j].push_back(f(i,k));
        }
    }
    rep(i,0,N) s.insert(f(i));
    int ans=-1;
    auto op=[&](auto self,int ind,int num,int val,int t) -> void {
        if(ans-val>=(N-ind)/2) return;
        if(ind==N){
            chmax(ans,val);
            return;
        }
        if(num&(1<<ind)){
            self(self,ind+1,num,val,0);
            return;
        }
        rep(k,0,8) if(!s.count(f(ind,k))){
            s.insert(f(ind,k));
            self(self,ind+1,num,val,0);
            s.erase(f(ind,k));
        }
        rep(i,ind+1,N) if((num&(1<<i))==0) for(auto x:G[ind][i]){
            if(!s.count(x)){
                s.insert(x);
                self(self,ind+1,num+(1<<i)+(1<<ind),val+1,1);
                s.erase(x);
            }
        }
    };
    op(op,0,0,0,1);
    if(ans==-1) cout<<ans<<"\n";
    else cout<<N-ans<<"\n";
}