#include <iostream>
#include <cstdio>
#include <string>
#include <algorithm>
#include <utility>
#include <cmath>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <functional>
using namespace std;
typedef long long ll;
typedef vector<ll> vl;
typedef vector<vector<ll>> vvl;
typedef pair<ll, ll> P;
typedef vector<vector<P>> vvP;
#define rep(i, n) for(ll i = 0; i < n; i++)
#define exrep(i, a, b) for(ll i = a; i <= b; i++)
#define out(x) cout << x << endl
#define exout(x) printf("%.10f\n", x)
#define chmax(x, y) x = max(x, y)
#define chmin(x, y) x = min(x, y)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define pb push_back
#define re0 return 0
const ll mod = 1000000007;
const ll INF = 1e16;
const ll MAX_N = 100010;

bool check(ll a, ll b, ll c) {
    if(a < 1 || b < 1 || c < 1) {
        return false;
    }
    if(a == b || b == c || c == a) {
        return false;
    }
    if( (a < b && b < c) || (a > b && b > c) ) {
        return false;
    }
    return true;
}

int main() {
    ll n;
    cin >> n;

    vl a(n);
    rep(i, n) {
        cin >> a[i];
    }

    ll ans = 0;
    rep(i, n-2) {
        if(check(a[i], a[i+1], a[i+2])) {
            ans++;
        }
    }

    out(ans);
    re0;
}