#include <algorithm>
#include <iostream>
#define max_size 10005


using namespace std;

int main(){
    int sum;
    cin >> sum;
    int num[max_size];
    int count = 0;
    for (int i = 0; i < sum; ++i)
    {
        cin>>num[i];
    }
    for (int i = 0; i < sum; ++i){
        if(((num[i]>num[i+1]) && (num[i+1]<num[i+2]))) count++;

        else if (((num[i]<num[i+1])&&(num[i+1]>num[i+2]))) count++;
        
        else 
        continue; 
    }
    cout<<count;
    return 0;
}