#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef string str;
int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    ll n;
    cin >> n;
    ll a[n], countt = 0;
    for (ll i = 0; i < n; i++) cin >> a[n];
    for (ll i = 1; i < n - 1; i++) if ((max({a[i-1], a[i], a[i+1]}) == a[i] || min({a[i-1], a[i], a[i+1]}) == a[i]) && a[i-1] != a[i+1] && a[i-1] != a[i] && a[i] != a[i+1]) countt++;
    cout << countt;
    return 0;
}