#include <iostream>
#include <iomanip>

#include <algorithm>
#include <math.h>

#include <string>
/////////
#define REP(i, x, n) for(int i = x; i < n; i++)
#define rep(i,n) REP(i,0,n)
#define P(p) cout<<(p)<<endl;
/////////
typedef long long LL;
typedef long double LD;
/////////
using namespace::std;
/////////

int main(void){
	cin.tie(0);
	ios::sync_with_stdio(false);
	cout << fixed;//
	//cout << setprecision(6);//

	int N;
	cin>>N;//[3,10^2]
	int A[100];
	rep(i,N){
		cin>>A[i];
	}
	int count = 0;
	rep(i,N-2){
		if( A[i] != A[i+1] && A[i+1] != A[i+2] && A[i+2] != A[i] &&
			(
				(A[i] < A[i+1] && A[i+2] < A[i+1])||
				(A[i] > A[i+1] && A[i+2] > A[i+1])
			)
		)
		{
			++count;
		}
	}
	P(count);
	return 0;
}