#include<bits/stdc++.h>
#define MAX 41
#define inf 1<<29
#define linf (1e16)
#define eps (1e-5)
#define Eps (1e-12)
#define mod 1000000007
#define pi acos(-1.0)
#define phi (1.0+sqrt(5.0))/2.0
#define f first
#define s second
#define mp make_pair
#define pb push_back
#define all(a) (a).begin(),(a).end()
#define pd(a) printf("%.10f\n",(double)(a))
#define pld(a) printf("%.10Lf\n",(ld)(a))
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define RFOR(i,a,b) for(int i=(a)-1;(b)<=i;i--)
#define Unique(v) v.erase(unique(all(v)),v.end())
#define equals(a,b) (fabs((a)-(b))<eps)
using namespace std;
typedef long double ld;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef pair<int,double> pid;
typedef pair<double,int> pdi;
typedef pair<double,double> pdd;
typedef vector<int> vi;
typedef vector<pii> vpi;

class Point{
public:
  double x,y;
  Point(double x=0,double y=0):x(x),y(y){}

  Point operator+(Point p){ return Point(x+p.x,y+p.y);}
  Point operator-(Point p){ return Point(x-p.x,y-p.y);}
  Point operator*(double k){ return Point(x*k,y*k);}
  Point operator/(double k){ return Point(x/k,y/k);}
  bool operator<(Point p)const{ return (x!=p.x ? x<p.x : y<p.y);}
  bool operator==(Point p)const{ return fabs(x-p.x)<eps && fabs(y-p.y)<eps;}

  double abs(){ return sqrt(norm());}
  double norm(){ return (x*x+y*y);}
};
typedef Point Vector;
typedef vector<Point> Polygon;

class Segment{
public:
  Point p1,p2;
  Segment(Point p1=Point(),Point p2=Point()):p1(p1),p2(p2){}
};
typedef Segment Line;

double norm(Vector a){ return (a.x*a.x+a.y*a.y);}
double abs(Vector a){ return sqrt(norm(a));}
double dot(Vector a,Vector b){ return (a.x*b.x+a.y*b.y);}
double cross(Vector a,Vector b){ return (a.x*b.y-a.y*b.x);}

int ccw(Point p0,Point p1,Point p2){
  Vector a=p1-p0;
  Vector b=p2-p0;
  if(cross(a,b)>eps)return 1;
  if(cross(a,b)<-eps)return -1;
  if(dot(a,b)<-eps)return 2;
  if(a.norm()<b.norm())return -2;
  return 0;
}

bool isParallel(Vector a,Vector b){
  return equals(cross(a,b),0.0);
}

bool isParallel(Segment s,Segment t){
  return equals(cross(s.p1-s.p2,t.p1-t.p2),0.0);
}

bool intersect(Line l,Segment s){
  if(ccw(l.p1,l.p2,s.p1)*ccw(l.p1,l.p2,s.p2)==1)return false;
  return true;
}

Point getCrossPointLL(Line a,Line b){
  double A=cross(a.p2-a.p1,b.p2-b.p1);
  double B=cross(a.p2-a.p1,a.p2-b.p1);
  if(abs(A)<eps)return b.p1;
  return b.p1+(b.p2-b.p1)*(B/A);
}

int contains(Polygon g,Point p){
  int n=g.size();
  bool x=false;
  for(int i=0;i<n;i++){
    Vector a=g[i]-p,b=g[(i+1)%n]-p;
    if(abs(cross(a,b))<eps && dot(a,b)<eps)return 1;
    if(a.y>b.y)swap(a,b);
    if(a.y<eps && eps<b.y && cross(a,b)>eps)x=!x;
  }
  if(x)return 2;
  return 0;
}

ull n;
Polygon P;
ull V[MAX] = {};

bool check(Point p1,Point p2){
  if(p1==p2)return true;
  Segment s1 = Segment(p1,p2);
  vector<pair<double,Point> > vp;
  vp.pb(mp(0.0,p1));
  vp.pb(mp(abs(p2-p1),p2));
  FOR(i,0,n){
    Segment s2(P[i],P[(i+1)%n]);
    if(isParallel(s1,s2))continue;
    if(!intersect(s1,s2))continue;
    Point C = getCrossPointLL(s1,s2);
    if(ccw(p1,p2,C)==0)vp.pb(mp(abs(C-p1),C));  
  }
  sort(all(vp));
  vp.erase(unique(all(vp)),vp.end());

  FOR(i,0,vp.size()-1){
    Point a=vp[i].s,b=vp[i+1].s;
    if(a==b)continue;
    Point m=a+(b-a)/2.0;
    if(contains(P,m)==0)return false;
  }
  return true;
}

int lim=0;

bool rec(ull S,ull T,int i,int d){
  if(n<i)return false;
  if(T == (1ll<<(n))-1 )return true;
  if(lim<=d)return false;
  else {
    if(rec(S,T,i+1,d))return true;
    ull NT = T|V[i],NS = S|(1ll<<i); 
    if(rec(NS,NT,i+1,d+1))return true;
  }
  return false;
}

int solve(){
  FOR(i,0,n)
    FOR(j,0,n)
      if(check(P[i],P[j]))V[i] |= (1ll<<j);
  FOR(i,1,n/3+1){
    lim = i;
    if(rec(0ll,0ll,0,0))return i;
  }
  return inf;
}

int main()
{
  cin>>n;
  P.resize(n);
  FOR(i,0,n)cin>>P[i].x>>P[i].y;
  cout<<solve()<<endl;
  return 0;
}

