#include<cstdio>
#include<cstring>
#include<vector>
#include<queue>
#include<algorithm>
#include<cmath>
#include<climits>
#include<string>
#include<set>
#include<map>
using namespace std;
#define rep(i,n) for(int i=0;i<((int)(n));i++)
#define reg(i,a,b) for(int i=((int)(a));i<=((int)(b));i++)
#define irep(i,n) for(int i=((int)(n))-1;i>=0;i--)
#define ireg(i,a,b) for(int i=((int)(b));i>=((int)(a));i--)
typedef long long int lli;
typedef pair<int,int> mp;
#define fir first
#define sec second
#define IINF INT_MAX
#define LINF LLONG_MAX

struct pos{
	double x,y;
	double norm,norm2;
	pos tov(pos a){
		return (a-(*this));
	}
	pos operator+(pos a)const{
		pos res=a;
		res.x+=x; res.y+=y;
		res=pos(res.x,res.y);
		return res;
	}
	pos operator-(pos a)const{
		pos res=(*this);
		res.x-=a.x; res.y-=a.y;
		res=pos(res.x,res.y);
		return res;
	}
	pos scalar(double a){
		pos res=(*this);
		res.x*=a; res.y*=a;
		res=pos(res.x,res.y);
		return res;
	}
	double dot(pos a){
		return x*a.x + y*a.y;
	}
	double cross(pos a){
		return x*a.y - y*a.x;
	}
	double theta(pos a){
		double nt=dot(a)/(norm*a.norm);
		nt=acos(max(-1.0,min(1.0,nt)));
		double ns=(cross(a)/(norm*a.norm));
		if(ns<0)nt*=-1;
		return nt;
	}
	pos(double ix,double iy){
		x=ix; y=iy;
		norm2=x*x+y*y;
		norm=sqrt(norm2);
	}
	pos(){}
	string str(){
		char ns[50];
		sprintf(ns,"(%lf %lf)",x,y);
		return	string(ns);
	}
	string html_str(){
		char ns[50];
		string res="";
		sprintf(ns,"ctx.arc(%lf,%lf,3,0,360);\n",x,y);
		res+="ctx.beginPath();\n" + string(ns) + "ctx.fill();\n";
		return res;
	}
	static pos polar(double r,double t){
		return pos(r*cos(t),r*sin(t));
	}
	bool  operator<(pos a) const{
		//if(x!=a.x)return (x<a.x);
		//return (y<a.y);
		if(y!=a.y)return (y<a.y);
		return (x<a.x);
	}	
	bool operator>(pos a)const{ return (a<(*this)); }	
};

struct line{
	pos p,q;
	pos vec;
	string str(){
		return ("("+p.str()+"-"+q.str()+")");
	}
	string html_str(){
		string res="";
		res+=p.html_str();
		res+=q.html_str();
		char ns[50];
		sprintf(ns,"ctx.moveTo(%lf,%lf);\n",p.x,p.y);
		res+="ctx.beginPath();\n"+string(ns);
		sprintf(ns,"ctx.lineTo(%lf,%lf);\n",q.x,q.y);
		res+=string(ns)+"ctx.stroke();\n";
		return res;
	}
	bool iscross(line a){
		double da,db;
		da=vec.cross( p.tov(a.p) );
		db=vec.cross( p.tov(a.q) );
		if(da*db>=0)return false;
		da=a.vec.cross( a.p.tov(p) );
		db=a.vec.cross( a.p.tov(q) );
		return (da*db<0);
	}
	line(pos ip,pos iq){
		p=ip; q=iq;
		vec=p.tov(q);
	}
	line(){}
	double dist(pos a){
		if(p.tov(a).dot( p.tov(q) )<0)return p.tov(a).norm;
		if(q.tov(a).dot( q.tov(p) )<0)return q.tov(a).norm;
		return abs(vec.cross(p.tov(a))/vec.norm);
	}
	double dist(line a){
		if(iscross(a))return 0;
		return min( min(dist(a.p),dist(a.q)) , min(a.dist(this->p),a.dist(this->q)));
	}
	pos crosspos(line a){
		double d1=a.vec.cross(a.p.tov(p));
		double d2=a.vec.cross(a.p.tov(q));
		//d1???ap-aq-bp?????¢???
		//d2???ap-aq-bq?????¢???
		//??¢??????????????´???b????????????????????????????????°?????????????????????????????????
		bool isna=(d1*d2<0);
		d1=abs(d1); d2=abs(d2);
		double sc;
		if(isna)sc = d1/(d1+d2); //???????????§??????????????????
		else{
			//if(d1>d2)sc = d1/(d1-d2);
			//else sc=-d1/(d2-d1);
			sc=d1/(d1-d2);
		}
		return (p+vec.scalar(sc));	
	}
};
double lowofcos_getcos(double a,double b,double c){
	return ((a*a+b*b-c*c)/(2*a*b));
}
struct circle{
	pos p;
	double r;
	line koten(circle a){
		pos cv=p.tov(a.p);
		double br=atan2(cv.y,cv.x);
		double dr=acos(lowofcos_getcos( r, cv.norm, a.r));
		pos p1= p+pos::polar(r,br+dr);
		pos p2= p+pos::polar(r,br-dr);
		if(p1>p2)swap(p1,p2);
		return line(p1,p2);
	}
	circle(pos ip,double ir){
		p=ip; r=ir;
	}
	circle(){}
};
struct polygon{
	vector<pos> ps;
	polygon(){}
	void input(int n){
		rep(i,n){
			double x,y;
			scanf("%lf%lf",&x,&y);
			ps.push_back(pos(x,y));
		}
	}
	double area(){
		double res=0;
		rep(i,ps.size()){
			pos no=ps[i],to=ps[(i+1)%ps.size()];
			res+=(no.x+to.x)*(no.y-to.y);
		}
		if(res<0)reverse(ps.begin(),ps.end());
		return abs(res)/2;
	}
	polygon(pos a,pos b){
		ps.push_back(a);
		ps.push_back(pos(a.x,b.y));
		ps.push_back(b);
		ps.push_back(pos(b.x,a.y));
	}
	line gete(int a){
		a%=ps.size();
		return line(ps[a],ps[(a+1)%ps.size()]);
	}
	int isin(pos a){//?????´??????2,?????£????????????1,?????????0
		double as=0;
		rep(i,ps.size()){
			line ne=gete(i);
			if(ne.dist(a)<=0)return 1;
			pos v1=a.tov(ne.p);
			pos v2=a.tov(ne.q);
			as+=v1.theta(v2);
		}
		if(abs(as)<1e-6)return 0;
		return 2;
	}
	polygon convex_full(){
		polygon res;
		int ns=ps.size();
		vector<pos> vs(2*ns);
		sort(ps.begin(),ps.end());
		int k=0;
		rep(i,ns){
			pos np=ps[i];
			while(k>1 && vs[k-2].tov(vs[k-1]).cross(vs[k-1].tov(np))<-1e-6)k--;
			vs[k]=np; k++;
		}
		int t=k;
		ireg(i,0,ns-2){
			pos np=ps[i];
			while(k>t && vs[k-2].tov(vs[k-1]).cross(vs[k-1].tov(np))<-1e-6)k--;
			vs[k]=np; k++;
		}
		vs.resize(k-1);
		swap(vs,res.ps);
		return res;
	}
	polygon cut(line a){//???????????????????????????
		polygon res;
		rep(i,ps.size()){
			line ne=gete(i);
			double d1=a.vec.cross(a.p.tov(ne.p));
			double d2=a.vec.cross(a.p.tov(ne.q));
			if(d1<1e-6)res.ps.push_back(ne.p);
			if(d1*d2<1e-6)res.ps.push_back(a.crosspos(ne));
		}
		return res;
	}
	polygon mult(polygon a){
		return a;
	}
};

pos randpos(){
	return pos(rand()%100,rand()%100);
}
line randline(){
	return line(randpos(),randpos());
}


void makehtml(char* name,string s){
	char fname[100];
	sprintf(fname,"%s.html",name);
	freopen(fname,"w",stdout);
	printf("<html>\n<head>\n<title>");
	printf("%s",name);
	printf("</title>\n</head>\n<body>\n");
	
	printf("<p>name: %s</p>",name);
	
	printf("<canvas id=\"vis\" width=\"%d\" height=\"%d\"></canvas>",500,500);
	
	printf("<script>\n");
	
	printf("var vis = document.getElementById('vis');\nvar ctx = vis.getContext('2d');\n");

	printf("%s",s.c_str());
	
	//ctx.fillStyle = \"rgb(0,0,0)\";
	

	
	printf("</script>\n");
	
	printf("</body>\n</html>\n");
}


int main(void){
	/*
	int n;
	scanf("%d",&n);
	polygon pol;
	rep(i,n){
		double x,y;
		scanf("%lf%lf",&x,&y);
		pol.ps.push_back(pos(x,y));
	}
	int q;
	scanf("%d",&q);
	rep(i,q){
		double x,y;
		scanf("%lf%lf",&x,&y);
		pos p1(x,y);
		scanf("%lf%lf",&x,&y);
		pos p2(x,y);
		line nl(p2,p1);
		polygon tp=pol.cut(nl);
		printf("%lf\n",tp.area());
	}
	*/
	int n;
	for(;;){
		scanf("%d",&n);
		if(n==0)break;
		polygon pol;
		rep(i,n){
			double x,y;
			scanf("%lf,%lf",&x,&y);
			pol.ps.push_back(pos(x,y));
		}
		polygon tp=pol.convex_full();
		int ans=0;
		rep(i,pol.ps.size()){
			pos np=pol.ps[i];
			if(tp.isin(np)==2)ans++;
		}
		printf("%d\n",ans);
	}
	/*
	rep(i,10){
		line l1=randline();
		line l2=randline();
		pos xp=l1.crosspos(l2);
		//printf("%s\n",l1.str().c_str());
		//printf("%s\n",l2.str().c_str());
		//printf("%s\n",xp.str().c_str());
		printf("%lf\n",l1.p.tov(xp).cross(l1.vec));
		printf("%lf\n",l2.p.tov(xp).cross(l2.vec));
	
	}
	return 0;
	*/
	
	/*
	string h="";
	h+=l1.html_str();
	h+=l2.html_str();
	h+=xp.html_str();
	
	
	
	makehtml("tess",h);	*/
	return 0;
}

Measured memory_bytes: 1136