#include<bits/stdc++.h>
#define st first
#define nd second
using namespace std;
typedef long long ll;
typedef long double ld;
struct pii{
int x, y;
pii(int x, int y): x(x), y(y){}
pii operator -(pii a){return pii(x-a.x, y-a.y);}
bool operator <(pii a){return (x<a.x || (x==a.x && y<a.y));}
bool operator ==(pii a){return x==a.x && y==a.y;}
ld dl(){return sqrt(x*1ll*x+y*1ll*y);}
};
ll cross(pii a, pii b){
return a.x*1ll*b.y-a.y*1ll*b.x;
}
ll cross(pii a, pii b, pii c){
return cross(b-a, c-a);
}
int sgn(ll a){
if(a==0)return 0;
return a/abs(a);
}
ll dot(pii a, pii b){
return a.x*1ll*b.x+b.y*1ll*a.y;
}
ll dot(pii a, pii b, pii c){
return dot(b-a, c-a);
}
typedef pair<pii, pii> odc;
vector<pii> V;
bool check(odc tt){
vector<ld> A, B;
for(int i=0; i<V.size(); i++){
ll t=sgn(cross(tt.st, V[i], tt.nd));
if(t>0){
A.push_back(dot(tt.st, tt.nd, V[i])/(V[i]-tt.st).dl());
B.push_back(dot(tt.nd, tt.st, V[i])/(V[i]-tt.nd).dl());
}
}
sort(A.begin(), A.end());
sort(B.begin(), B.end());
//cout<<tt.st.x<<" "<<tt.st.y<<" "<<tt.nd.x<<" "<<tt.nd.y<<"\n";
//cout<<A.size()<<"\n";
for(int i=0; i<V.size(); i++){
ll t=sgn(cross(tt.st, V[i], tt.nd));
if(t<0){
ld k=dot(tt.st, tt.nd, V[i])/(V[i]-tt.st).dl(), l=dot(tt.nd, tt.st, V[i])/(V[i]-tt.nd).dl();
k=-k;
l=-l;
if(lower_bound(A.begin(), A.end(), k)-A.begin()+lower_bound(B.begin(), B.end(), l)-B.begin()!=A.size()){
return 0;
}
}
}
return 1;
}
pair<vector<pii>, vector<pii> > hull(){
sort(V.begin(), V.end());
vector<pii> ans, ans2;
sort(V.begin()+1, V.end(), [](pii A, pii B){return cross(A-V[0], B-V[0])>0;});
ans.push_back(V[0]);
ans.push_back(V[1]);
//for(int i=0; i<V.size(); i++)cout<<V[i].x<<" "<<V[i].y<<"\n";
for(int i=2; i<V.size(); i++){
while(ans.size()>=2 && cross(ans.back(), ans[ans.size()-2], V[i])>0){
ans2.push_back(ans.back());
ans.pop_back();
}
ans.push_back(V[i]);
}
return {ans, ans2};
}
typedef array<pii, 3> tri;
int main(){
int n;
cin>>n;
V.resize(n, pii(0, 0));
for(pii &i:V){
cin>>i.x>>i.y;
}
auto h=hull();
assert(h.st.size()>2);
//cout<<h.st.size();
vector<tri> tra;
for(int i=2; i<h.st.size(); i++){
tra.push_back({h.st[0], h.st[i-1], h.st[i]});
}
//cout<<tra.size();
for(pii i:h.nd){
bool b=0;
for(int j=0; j<tra.size(); j++){
int a1=sgn(cross(i, tra[j][0], tra[j][1])),a2=sgn(cross(i, tra[j][1], tra[j][2])),a3=sgn(cross(i, tra[j][2], tra[j][0]));
if(a1==a2 && a2==a3){
b=1;
tra.push_back({i, tra[j][0], tra[j][1]});
tra.push_back({i, tra[j][1], tra[j][2]});
tra.push_back({i, tra[j][2], tra[j][0]});
swap(tra[j], tra.back());
tra.pop_back();
break;
}
}
assert(b==1);
}
//cout<<tra.size();
vector<odc> todo;
for(auto i:tra){
todo.push_back({i[0], i[1]});
todo.push_back({i[1], i[2]});
todo.push_back({i[2], i[0]});
}
for(auto &i:todo){
if(i.st<i.nd)swap(i.st, i.nd);
}
sort(todo.begin(), todo.end(), [](odc a, odc b){return a.st<b.st || (a.st==b.st && a.nd<b.nd);});
int ans=0;
for(int i=0; i<todo.size(); i++){
if(i==0 || !(todo[i].st==todo[i-1].st) || !(todo[i].nd==todo[i-1].nd)){
//cout<<"a";
ans+=check(todo[i]);
}
}
cout<<ans;
}
