#include <bits/stdc++.h>
using namespace std;
signed main(){
    int n;
    cin >> n;
    vector<int> a(n);
    for(auto &to : a)cin >> to;
    int ans = 0;
    for(int i=0;i<n-2;i++){
        set<int> s;
        for(int j=i;j<i+3;j++){
            s.insert(a[j]);
        }if(s.size() == 3 && (a[i] > a[i+1] && a[i+2] > a[i+1]||a[i] < a[i+1] && a[i+2] < a[i+1]))ans++;
    }cout << ans << '\n';
    return 0;
}