# include <stdio.h>
int main ( )
{
	int n, m[10001]={0},js=0;
	scanf ("%d",&n);
	for (int i=1; i<=n; i++){
		scanf ("%d",&m[i]);
	}
	for (int i=1; i<=n-2; i++){
		if (m[i]>=m[i+1]&&m[i+1]<=m[i+2]){//判断波谷并计数//
			js++;
		}
		if (m[i]==m[i+1]){//去掉像0，0；1，1，1这样所造成的重复// 
			js-=1;
		}
	}
	printf ("%d",js);
	
	
	return 0;
}