纯模拟，枚举所有数，注意第一个和最后一个是不算的

#include <bits/stdc++.h>
//#pragma GCC optimize(2)
//#define int long long
#define endl '\n'
using namespace std;
int a[1005];
int n;
signed main()
{
    ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);

	cin >> n;
	for(int i = 1; i <= n; i++)
	{
		cin >> a[i];
	}
	
	int ans = 0;
	for(int i = 2; i <= n-1; i++)
	{
		if(a[i]>a[i-1]&&a[i]>a[i+1])ans++;
		if(a[i]<a[i-1]&&a[i]<a[i+1])ans++;
	}
	cout << ans << endl;
    return 0;
}