#include <iostream>
#include <algorithm>
using namespace std;
int main()
{
    int n, a[100];
    while (cin>>n) {
        for(int i=0;i<n;++i) cin>>a[i];
        int res=0;
        for(int i=0;i+2<n;++i)
            if (a[i]!=a[i+1] and a[i+1]!=a[i+2] and a[i+2]!=a[i] and
                (max({a[i], a[i+1], a[i+2]})==a[i+1] or min({a[i], a[i+1], a[i+2]})==a[i+1]))
                ++res;
        cout<<res<<endl;
    }
}