#include<bits/stdc++.h> using namespace std; #define vi vector<int> #define vvi vector<vi> #define vs vector<string> #define pb push_back #define P pair<int,int> #define vp vector<P> #define PP pair<P,int> #define vpp vector<PP> #define fi first #define se second #define INF (1<<30) #define MOD 1000000007 #define REP(i,n) for(int i=0;i<n;i++) #define REPR(i,n) for(int i=n;i>=0;i--) #define FOR(i,m,n) for(int i=m;i<n;i++) #define all(x) (x).begin(),(x).end() int main(){ int n; cin>>n; vi d(n); REP(i,n)cin>>d[i]; int ans=0; REP(i,n-2){ int a=0,b=0; if(d[i]>d[i+1])a++; if(d[i]>d[i+2])a++; if(d[i+2]>d[i])b++; if(d[i+2]>d[i+1])b++; if(a==1||b==1){ ans++; }else if(d[i]!=d[i+1]&&d[i]!=d[i+2]&&d[i+1]!=d[i+2]){ ans++; } } cout<<ans<<endl; return 0; }