#include<bits/stdc++.h>
using namespace std;
#define ri register int
typedef long long ll;
const int maxn=1e5+10;
inline ll sqr(ll k){return k*k;}
struct vec{
	ll x,y;
	inline vec(ll x_=0,ll y_=0):x(x_),y(y_){}
	inline vec operator-(const vec &k){
		return vec(x-k.x,y-k.y);
	}
	inline bool operator<(const vec &k)const{
		return x!=k.x?x<k.x:y<k.y;
	}
	inline ll cross(const vec &k){
		return x*k.y-y*k.x;
	}
	inline ll norm(){
		return x*x+y*y;
	}
	inline ll dist(const vec &k){
		return sqrt(sqr(x-k.x)+sqr(y-k.y));
	}
}a[maxn],st[maxn];
inline bool cmp(const int &x,const int &y){
	ll det=(a[x]-a[1]).cross(a[y]-a[1]);
	return det?det>0:(a[x]-a[1]).norm()<(a[y]-a[1]).norm();
}
int n,id[maxn],tp;
inline int graham(){
	int ret=0;
	for(int T=1;T<=10;++T){
		ri cnt=0,x=rand()%n+1;
		if(x>1)swap(a[1],a[x]);
		iota(id+1,id+n+1,1);
		sort(id+2,id+n+1,cmp);
		st[tp=1]=a[1];
		for(ri i=2;i<=n;++i){
			ri j=id[i];
			if(tp>1&&(a[j]-st[tp-1]).cross(st[tp]-st[tp-1]))cnt+=3,tp-=2;
			else st[++tp]=a[j];
		}
		ret=max(ret,cnt);
	}
	return ret;
}
int main(){
	srand(time(0));
	while(~scanf("%d",&n)){
		for(ri i=1;i<=n;++i)scanf("%lld%lld",&a[i].x,&a[i].y);
		printf("%d\n",n-graham());
	}
	return 0;
}