#include <iostream>
using namespace std;
int main(){
    int N,A[100],cnt=0;
    cin >> N;
    for(int i=0;i<N;i++)cin >> A[i];
    for(int mid=1;mid+1<N;mid++){
        if((A[mid]-A[mid-1])*(A[mid]-A[mid+1])>0 && A[mid-1]!=A[mid+1])cnt++;
    }
    cout << cnt << endl;
    return 0;
}