#include<bits/stdc++.h>
using namespace std;
const double eps = 1e-6;
const double PI = acos(-1);
const int maxn = 100010;
typedef struct{double x,y;} pos;
typedef struct{pos st,ed;} line;
inline int sign(double x){
    if(fabs(x)<eps) return 0;
    else if(x > eps) return 1;
    else return -1;
}
inline int dcmp(double x,double y){
    if(fabs(x-y)<eps) return 0;
    else if(x > y) return 1;
    else return -1;
}
pos operator +(pos a,pos b){return{a.x+b.x,a.y+b.y};}
pos operator -(pos a,pos b){return{a.x-b.x,a.y-b.y};}
pos operator *(pos a,double k){return {a.x*k,a.y*k};}
pos operator /(pos a,double k){return {a.x/k,a.y/k};}
double operator*(pos a,pos b){return a.x*b.y-a.y*b.x;}
double operator&(pos a,pos b){return a.x*b.x+a.y*b.y;}
pos pl[maxn]; 
int n,m,q[maxn]; 
line ln[maxn];
double get_angle(line a){
    pos st = a.st,ed = a.ed;
    return atan2(ed.y-st.y,ed.x-st.x);
}
inline double area(pos a ,pos b,pos c){
    return (b - a) * (c - a);
}
inline bool cmp(line a,line b){
    return get_angle(a) < get_angle(b);
}
pos line_intersection(pos p,pos v,pos q,pos w){
    pos u = p - q;
    double t = (w * u) / (v * w);
    return {p.x+v.x*t,p.y+v.y*t}; 
}
pos line_intersection(line a,line b){
    return line_intersection(a.st,a.ed-a.st,b.st,b.ed-b.st);
}
bool on_right(line& a,line& b,line& c){
    pos o = line_intersection(b,c);
    return sign(area(a.st,a.ed,o)) <= 0;
}
bool halfplaneintersection(int cnt){
    sort(ln,ln+cnt,cmp);
    int hh = 0,tt = 0;
   // cout << cnt << endl;
    for(int i = 0 ; i < cnt ; i ++){
        if(!i&&!dcmp(get_angle(ln[i]),get_angle(ln[i-1]))) continue;
        while(hh<tt&&on_right(ln[i],ln[q[tt-1]],ln[q[tt]])) tt -= 1;
        while(hh<tt&&on_right(ln[i],ln[q[hh]],ln[q[hh+1]])) hh += 1;
        q[++tt] = i;
    }
    //printf("mid = 1 :: %d %d\n",hh,tt);
    while(hh<tt&&on_right(ln[hh],ln[q[tt-1]],ln[q[tt]])) tt -= 1;
    while(hh<tt&&on_right(ln[tt],ln[q[hh]],ln[q[hh+1]])) hh += 1;
    //q[++tt] = q[hh];
    //printf("mid = 1 :: %d %d\n",hh,tt);
    if(hh>=tt) return false;
    else return true;
}
bool check(int mid){
    int cnt = 0;
    for(int i = 1  ; i <= n ; i ++){
        int xx = i,yy = (i + mid) % n;
        ln[cnt++] = (line){pl[yy],pl[xx]};
    }    
    return halfplaneintersection(cnt);
}

int main(){
    while(scanf("%d",&n)==1&&n){
        memset(q,0,sizeof q);
        for(int i = 1 ; i <= n ; i ++) scanf("%lf%lf",&pl[i].x,&pl[i].y);
        int l = 1, r = n;
        while(l<=r){
            int mid = (l + r) >> 1;
            //cout << mid << endl;
            if(check(mid)) l = mid + 1; //如果半平面交非空
            else r = mid - 1;
        }
        printf("%d\n",l);
    }
    
    return 0;
}

板子应该没问题，谁看下为啥T了 15秒限制，而且udebug没有数据。