#include<cstdio>
#include <iostream>
#include<algorithm>
#include<string>
#include<queue>
#include<vector>
#include<functional>
#include<cmath>
#include<map>
#include<stack>
#include<set>
#include<numeric>

using namespace std;
typedef long long ll;
typedef pair<int, int> Pr;

int N;
int A[110];
int ans;

int main()
{
	cin >> N;
	for (int i = 0; i < N; i++)
		cin >> A[i];

	for (int i = 0; i < N-2; i++) {
		int mi = min(A[i], min(A[i + 1], A[i + 2]));
		int mx = max(A[i], max(A[i + 1], A[i + 2]));
 		if (A[i] == A[i + 1] || A[i] == A[i + 2] || A[i + 1] == A[i + 2])continue;
		if (A[i + 1] == mi || A[i + 1] == mx)ans++;
	}
	cout << ans << endl;
	return 0;
}