#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
using namespace std;
using std::cout;
using std::cin;
using std::endl;
using ll=__int128_t;
using ld=long double;
ll ILL=2167167167167167167;
const int INF=2100000000;
const int mod=998244353;
#define rep(i,a,b) for (ll i=a;i<b;i++)
#define all(p) p.begin(),p.end()
template<class T> using _pq = priority_queue<T, vector<T>, greater<T>>;
template<class T> ll LB(vector<T> &v,T a){return lower_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> ll UB(vector<T> &v,T a){return upper_bound(v.begin(),v.end(),a)-v.begin();}
template<class T> bool chmin(T &a,const T &b){if(a>b){a=b;return 1;}else return 0;}
template<class T> bool chmax(T &a,const T &b){if(a<b){a=b;return 1;}else return 0;}
template<class T> void So(vector<T> &v) {sort(v.begin(),v.end());}
template<class T> void Sore(vector<T> &v) {sort(v.begin(),v.end(),[](T x,T y){return x>y;});}
void yneos(bool a){if(a) cout<<"Yes\n"; else cout<<"No\n";}
template<class T> void vec_out(vector<T> &p){for(int i=0;i<(int)(p.size());i++){if(i) cout<<" ";cout<<p[i];}cout<<"\n";}
template<class T> T vec_min(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmin(ans,x);return ans;}
template<class T> T vec_max(vector<T> &a){assert(!a.empty());T ans=a[0];for(auto &x:a) chmax(ans,x);return ans;}
template<class T> T vec_sum(vector<T> &a){assert(!a.empty());T ans=a[0]-a[0];for(auto &x:a) ans+=x;return ans;}
int pop_count(long long a){int res=0;while(a){res+=(a&1),a>>=1;}return res;}

 


bool _2d_comp(pair<ll,ll> &l,pair<ll,ll> &r){
	if(l.first==0&&r.first==0){
		return l.second>0&&r.second<0;
	}
	if(l.first==0){
		return l.second>0||r.first<0;
	}
	if(r.first==0){
		return !(r.second>0||l.first<0);
	}
	if((l.first<0)^(r.first<0)) return l.first>0;
	return l.first*r.second<l.second*r.first;
}



void solve();
// oddloop
int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	
	int t=1;
	//cin>>t;
	rep(i,0,t) solve();
}

void solve(){
	int N;
	cin>>N;
	vector<ll> X(N),Y(N);
	rep(i,0,N){
		long long x,y;
		cin>>x>>y;
		X[i]=x,Y[i]=y;
	}
	int ans=0;
	rep(i,0,N){
		vector<pair<ll,ll>> p;
		rep(j,0,N){
			if(i==j) continue;
			p.push_back({X[i]-X[j],Y[i]-Y[j]});
		}
		sort(all(p),[&](pair<ll,ll> l,pair<ll,ll> r){
			return _2d_comp(l,r);
		});
		rep(j,0,N-2){
			if(_2d_comp(p[j],p[j+1])|_2d_comp(p[j+1],p[j])) continue;
			ans++;
			break;
		}
	}
	cout<<ans<<"\n";
}