#include <bits/stdc++.h>
using namespace std;

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
 
    int N; cin>> N;
    vector<int> A(N);
    for(auto &a : A) cin >> a,a--;

    int answer = 0;
    for(int i=0; i<N-2; i++){
        int a1 = A.at(i),a2 = A.at(i+1),a3 = A.at(i+2);
        if(set<int>{a1,a2,a3}.size() != 3) continue;
        if(a2 == max({a1,a2,a3}) || a2 == min({a1,a2,a3})) answer++;
    }
    cout << answer << endl;
}