#include <iostream>

using namespace std;

int countKadomatu(int num, int* a){
    int count = 0;
    for (int i = 0; i < num - 2; ++i) {
        if((a[i] > a[i+2] && a[i+2] > a[i+1]) || (a[i+1] > a[i] && a[i] > a[i+2])
        || (a[i+2] > a[i] && a[i] > a[i+1])   || (a[i+1] > a[i+2] && a[i+2] > a[i])){
            count++;
        }
    }
    return count;
}

void printKadomatu(int num, int* a){
    for(int i=0; i<num; i++){
        cout << a[i] << " ";
    }
}

int main() {
    int n;
    int len[105] = {0};

    cin >> n;
    for (int i = 0; i < n; ++i)
        cin >> len[i];

    //printKadomatu(n, len);
    cout << countKadomatu(n, len) << endl;

    return 0;
}