#include <bits/stdc++.h> using namespace std; #define REP(i, n) for(int i=0, i##_len=(n); i<i##_len; ++i) #define REPR(i, n) for(int i = n;i >= 0;i--) #define REP3(i, m, n) for(int i = m, i##_len=(n);i < i##_len;i++) #define FORVEC(i, v) for(int i = 0;i < v.size();i++) #define INF 1000000000 #define pb(a) push_back(a) #define llong long long int main(){ int a[100]; int n; int ans=0; cin>>n; REP(i,n){ cin>>a[i]; } REP(i,n-2){ if(a[i]==a[i+1])continue; if(a[i]==a[i+2])continue; if(a[i+1]==a[i+2])continue; if((a[i]>a[i+1]&&a[i]<a[i+2])||(a[i]<a[i+1]&&a[i]>a[i+2])){ ans++; } if((a[i+2]>a[i+1]&&a[i+2]<a[i])||(a[i+2]<a[i+1]&&a[i+2]>a[i])){ ans++; } } cout<<ans<<endl; return 0; }