#include<bits/stdc++.h>
#define ll long long
using namespace std;
const int N=1e5+100;
set<int> s;
struct Point{
int x,y;
}p[N];
Point ch[N];
bool cmp(Point x,Point y){
return x.x<y.x||(x.x==y.x&&x.y<y.y);//x从小到大排序，如果x相同则y从小到大排序
}
int Cross(Point x,Point y,Point z){
ll x1=x.x-y.x;
ll y1=x.y-y.y;
ll x2=z.x-y.x;
ll y2=z.y-y.y;
if((x1*y2-x2*y1)<=0) return 0;//在右边（关于 2. ）
return 1;
}
int main(){
int n;scanf("%d",&n);
for(int i=0;i<n;i++){
scanf("%d%d",&p[i].x,&p[i].y);
}
//sort(p,p+n,cmp);
int m=0;
//从左到右扫描
for(int i=0;i<n;i++){
bool f=false;
while(m>1&&!Cross(ch[m-1],ch[m-2],p[i])){
f=true;
m--;
}
if(!f&&i>1) s.insert(ch[m-1].x);
ch[m++]=p[i];
}
cout<<s.size()<<endl;
return 0;
}
