#include <bits/stdc++.h>
#define be(v) (v).begin(),(v).end()
#define pb(q) push_back(q)
#define rep(i, n) for(int i=0;i<n;i++)
#define all(i, v) for(auto& i : v)
typedef long long ll;
using namespace std;
const ll mod=1000000007, INF=(1LL<<60);
#define doublecout(a) cout<<fixed<<setprecision(10)<<a<<endl;

int main() {
    cin.tie(0);
    cout.tie(0);
    ios::sync_with_stdio(false); 
    int n;
    cin >> n;
    vector<int> a(n);
    rep(i, n) cin >> a[i];
    int ans = 0;
    rep(i, n - 2) {
        set<int> s;
        rep(j, 3) s.insert(a[i+j]);
        if(s.size() == 3) {
            if(*s.begin() == a[i + 1] || *s.rbegin() == a[i + 1]) {
                ans ++;
            }
        }
    }
    cout << ans << endl;
    return 0; 
}