#include<bits/stdc++.h>

using namespace std;

struct P{
	int x, y;

	P operator+(P p) { return {x + p.x, y + p.y};}
	P operator-(P p) { return {x - p.x, y - p.y};}

	int dot(P p){ return x * p.x + y * p.y; }
	int det(P p){ return x * p.y - y * p.x; }
};

signed main(){
	ios::sync_with_stdio(false);
	cin.tie(nullptr);

	int n;
	cin >> n;

	vector<P> p(n);
	for(int i = 0; i < n; i++)
		cin >> p[i].x >> p[i].y;

	int s = 0;

	for(int i = 0; i < n; i++)
		if(p[i].y < p[s].y)
			s = i;

	int ans = 0, l = s, r = s;

	P cur = p[(r + 1) % n] - p[r];
	while(cur.y >= 0 || cur.x < 0){
		// cerr << r << " " << cur.x << " " << cur.y << "\n";
		r = (r + 1) % n;
		cur = p[(r + 1) % n] - p[r];
	}

	cur = p[(n + l - 1) % n] - p[l];
	while(l != r){
		while(l != r && (cur.y >= 0 || cur.x > 0)){
			// cerr << l << " " << cur.x << " " << cur.y << "\n";
			l = (n + l - 1) % n;
			cur = p[(n + l - 1) % n] - p[l];
		}
		if(l != r) 
			l = (n + l - 1) % n;
		ans++;
	}

	cout << ans;

	return 0;
}