#include<bits/stdc++.h>
using namespace std;
#define int long long
#define pii pair<int,int>
void solve() {
	int n;
	cin >> n;
	vector<pii> a;
	for (int i = 0; i < n; i++) {
		int x, y;
		cin >> x >> y;
		a.push_back({ x,y });
	}
	for (int i = 0; i < n; i++)
		a.push_back(a[i]);
	int ans = 0;
	int f = 0;
	int p = n;
	for (int i = 1; i <= 2*n-1;i++) {
		if (i == p + n)
			break;
		if (a[i - 1].first <= a[i].first) {
			if (f && a[i - 1].second < a[i].second)	{
				f = 0, ans++;
				p = min(p, i);
			}
			if (a[i - 1].second > a[i].second)
				f = 1;
		}
		else
			f = 0;
	}
	cout << ans << '\n';
}
signed main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	cout.tie(nullptr);
	int t = 1;
	//cin >> t;
	while (t--)
		solve();
	return 0;
}