#include <cstdio>
#include <algorithm>

using namespace std;

int n;
int dat[100];

int main()
{
  scanf("%d",&n);
  for (int i = 0; i < n; i++) {
    scanf("%d",&dat[i]);
  }
  int ans = 0;
  for (int i = 0; i+2 < n; i++) {
    int arr[3] = {dat[i],dat[i+1],dat[i+2]};
    sort(arr,arr+3);
    if (arr[1] == dat[i] || arr[1] == dat[i+2]) {
      if (arr[0] != arr[1] && arr[0] != arr[2] && arr[1] != arr[2]) {
        ans ++;
      }
    }
  }
  printf("%d\n",ans);
  return 0;
}