#include <bits/stdc++.h>
#define LL long long
const int N = 2e5 + 3;
struct point{
    LL x,y;
    void read(){
        LL a,b;
        scanf("%lld%lld",&a,&b);
        x = a,y = b;
    }
    point(LL x = 0,LL y = 0) : x(x),y(y){}
    point operator+(const point &r)const{return point(x + r.x,y + r.y);}
    point operator-(const point &r)const{return point(x - r.x,y - r.y);}
    LL operator*(const point&r){return x * r.y - y * r.x;}
}p[N],s[N];
int n,top;

int main()
{
   // freopen("a.txt","r",stdin);
    while(scanf("%d",&n) != EOF){
        top = 0;
        for(int i = 1;i <= n;++i){
            p[i].read();

            if(top >= 2 && (s[top - 1] - s[top - 2]) * (p[i] - s[top - 1]) != 0){

                top -= 2;
            }
                else s[++top] = p[i];
         //   printf("GG");
        }
     //   printf("top:%d\n",top);
        if(top < 3) printf("%d\n",top);
        else{
            int sum = 0;
            for(int i = 1;i <= n;++i){
                if(((s[1] - s[2]) * (s[1] - p[i])) == 0) sum++;
            }
            printf("%d\n",std::max(0,n - (n - sum) * 3));
        }

    }
    return 0;
}