#include <bits/stdc++.h>
using namespace std;

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);  
	int n;
	cin >> n;
	vector<int> a(n);
	for(int i = 0; i < n; i++) {
		cin >> a[i];
	}
	int ans = 0;
	for(int i = 0; i <= n - 3; i++) {
		int x = a[i];
		int y = a[i + 1];
		int z = a[i + 2];
			cerr << x << " " << y << " " << z << endl;
		if(x == y || y == z || z == x) continue;
		int mi = min(x, min(y, z));
		int mx = max(x, max(y, z));
		if(mi == y || mx == y) ans++;
	}
	cout << ans << endl;
	return 0;	
}