#include<bits/stdc++.h>
using namespace std;
using ll=long long;
using vec=complex<int>;
ll dot(vec a,vec b){
    return 1ll*real(a)*real(b)+1ll*imag(a)*imag(b);
}
ll cross(vec a,vec b){
    return 1ll*real(a)*imag(b)-1ll*imag(a)*real(b);
}
int find(vec a){
    if(imag(a))return imag(a)>0?1:3;
    else return real(a)>0?0:2;
}
bool comp(vec a,vec b){
    int t=find(a),s=find(b);
    if(t!=s)return t<s;
    return cross(a,b)>0;
}
const int N=2e3+10;
int n;
vec a[N];
bool cmp(vec a,vec b){
    return real(a)!=real(b)?real(a)<real(b):imag(a)<imag(b);
}
int k,id[N],stk[N];
bool chk(vec a,vec b,vec c){
    // cerr<<a<<' '<<b<<' '<<c<<endl;
    return cross(c-b,a-b)>0;
}
void convex(){
    sort(a+2,a+1+n,[&](vec x,vec y){
        return comp(x-a[1],y-a[1]);
    });
    stk[k=1]=1;
    for(int i=2;i<=n;i++){
        for(;k>1&&!chk(a[stk[k-1]],a[stk[k]],a[i]);k--);
        stk[++k]=i;
    }
    // for(int i=1;i<=n;i++)cerr<<a[i]<<"\n "[i<n];
    // cerr<<k<<endl;
    for(int i=1;i<=k;i++)id[stk[i]]=i;
}
int main(){
    cin>>n;
    for(int i=1,x,y;i<=n;i++){
        cin>>x>>y,a[i]=vec(x,y);
    }
    sort(a+1,a+1+n,cmp);
    convex();
    int ans=1;
    for(int i=1;i<=n;i++)if(!id[i]){
        static int cur[N];
        for(int j=1;j<=n;j++)if(i!=j)cur[j-(j>i)]=j;
        sort(cur+1,cur+n,[&](int x,int y){
            return comp(a[x]-a[i],a[y]-a[i]);
        });
        for(int i=1;i<n;i++){
            if(id[cur[i]]&&id[cur[i%(n-1)+1]])ans++;
        }
    }
    cout<<ans<<endl;
	return 0;
}