#include <bits/stdc++.h>
using namespace std;
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include "trilib.h"
/*
static int n;
static long long *x, *y;
static int queries=0;
static void init() {
static int is_inited=0;
if (is_inited)
return;
is_inited=1;
assert(scanf("%d", &n)==1);
x=(long long*)malloc((n+1)*sizeof(long long));
y=(long long*)malloc((n+1)*sizeof(long long));
for (int i=1; i<=n; i++)
assert(scanf("%lld%lld", &x[i], &y[i])==2);
}
int get_n() {
init();
return n;
}
int is_clockwise(int a, int b, int c) {
init();
assert(a>=1 && a<=n);
assert(b>=1 && b<=n);
assert(c>=1 && c<=n);
assert(a!=b && a!=c && b!=c);
queries++;
if(queries == 1000 * 1000 + 1)
printf("Too many queries!");
return (x[b]-x[a])*(y[c]-y[a])-(x[c]-x[a])*(y[b]-y[a])<0;
}
void give_answer(int s) {
init();
printf("%d\n", s);
}*/
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(0);
int n=get_n();
int v=-1;
for(int i=3; i<=n; i++){
if(is_clockwise(1, 2, i)){
if(v==-1) v=i;
else if(is_clockwise(2, i, v)){
v=i;
}
}
}
// v is on the borders
int u=-1;
for(int i=1; i<=n; i++){
if(i==v||i==2) continue;
if(is_clockwise(2, v, i)){
if(u==-1) u=i;
else if(is_clockwise(v, i, u)){
u=i;
}
}
}
vector<int> vis(n+1);
vis[u]=1;
vis[v]=1;
int flag=1;
while(flag){
flag=0;
for(int i=1; i<=n; i++){
if(i==u || i==v) continue;
if(is_clockwise(v, u, i)){
if(flag==0) flag=i;
else if(is_clockwise(u, i, flag)){
flag = i;
}
}
}
if(vis[flag]||flag==0) break;
vis[flag] = 1;
v=u; u=flag;
}
int ans=0;
for(auto i: vis) ans+=i;
give_answer(ans);
}
