#include<bits/stdc++.h>
using namespace std;
int main(){
    int n,ans=0;
    cin>>n;
    vector<int> a(n);
    for(int i=0;i<n;++i)cin>>a[i];
    for(int i=1;i<n-1;++i){
        if(a[i-1]==a[i]||a[i]==a[i+1]||a[i+1]==a[i-1])continue;
        if(a[i]==min({a[i-1],a[i],a[i+1]})||a[i]==max({a[i-1],a[i],a[i+1]}))++ans;
    }
    cout<<ans<<endl;
}