#include<bits/stdc++.h>
using namespace std;
int n;
struct VECTOR
{
	int x,y;
	int operator*(const VECTOR &v)const
	{
		return x*v.x+y*v.y;
	}
	int operator^(const VECTOR &v)const
	{
		return x*v.y-y*v.x;
	}
};
struct POINT
{
	int x,y;
	VECTOR operator-(const POINT &p)const
	{
		return {x-p.x,y-p.y};
	}
	bool operator<(const POINT &p)const
	{
		if(x==p.x)return y<p.y;
		else return x<p.x;
	}
	bool operator==(const POINT &p)const
	{
		return x==p.x&&y==p.y;
	}	
}p[2005],p1[2005];
vector<POINT> st;
bool cmp1(POINT p1,POINT p2)
{
	if(p1.x==p2.x)return p1.y<p2.y;
	else return p1.x<p2.x;
}
bool check(POINT p)
{
	POINT back1=st.back(),back2=*(st.rbegin()+1);
	return ((back1-back2)^(p-back1))<=0;
}
void andrew()
{
	sort(p+1,p+n+1,cmp1);
	for(int i=1;i<=n;i++)
	{
		while(st.size()>1&&check(p[i]))st.pop_back();
		st.push_back(p[i]);
	}
	int k=st.size();
	for(int i=n-1;i>=1;i--)
	{
		while(st.size()>k&&check(p[i]))st.pop_back();
		st.push_back(p[i]);
	}
	if(st.size()>1)st.pop_back();
}
POINT o;
int find_zone(POINT p)
{
	int x=p.x-o.x,y=p.y-o.y;
	if(y<0)return 1;
	if(y==0&&x>0)return 2;
	if(y==0&&x==0)return 3;
	if(y>0)return 4;
	if(y==0&&x<0)return 5;
    return 0;
}
bool cmp2(POINT p1,POINT p2)
{
	int z1=find_zone(p1),z2=find_zone(p2);
	if(z1!=z2)return z1<z2;
	else
	{
		VECTOR v1=p1-o,v2=p2-o;
		if((v1^v2)==0)return v1*v1>v2*v2;
		else return (v1^v2)>0;
	}
}
map<POINT,POINT> mp;
void solve()
{
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>p[i].x>>p[i].y;
		p1[i]=p[i];
	}
	andrew();
	for(int i=0;i<st.size();i++)
		mp[st[i]]=st[(i+1)%st.size()];
	int add=0;
	for(int i=1;i<=n;i++)
	{
		if(mp.find(p1[i])!=mp.end())continue;
		o=p1[i];
		int m=0;
		for(int j=1;j<=n;j++)
			if(j!=i)p[++m]=p1[j];
		sort(p+1,p+m+1,cmp2);
		
		POINT last;
		for(int j=1;j<n;j++)
		{
			int pre=j-1;
			if(j==1||((p[j]-o)^(p[j-1]-o))!=0)
			{
				if(j!=1)
				{
					if(mp.find(last)!=mp.end()&&mp[last]==p[j])
					{
						add++;
					}
				}
				last=p[j];
			}
		}
		if(mp.find(last)!=mp.end()&&mp[last]==p[1])add++;
	}
	cout<<add+1<<endl;
}
signed main()
{
	ios::sync_with_stdio(false),cin.tie(0),cout.tie(0);
	solve();
	return 0;
}
/*
7
1 4
4 0
2 3
3 1
3 5
0 0
2 4

*/