#include <iostream>
#include <algorithm>
#include <string>
#include <cstring>
using namespace std;

#define REP(i,a,b) for(i=a;i<b;i++)
#define rep(i,n) REP(i,0,n)
#define SQR(X) ((X)*(X))

typedef long long ll;
typedef unsigned long long ull;
typedef long double lb;
/* ここからが本編 */

int main(void)
{
  int i,j;
  int n;
  int a,b,c;
  int cnt = 0;
  int max1,max2;
  cin >> n;
  cin >> a >> b;

  rep(i,n-2) {
    cin >> c;
    if(a == b || b == c || c == a) ;
    else {
      max1 = a;
      if(max1 < b) {
        max2 = max1;
        max1 = b;
      }
      else max2 = b; 
      if(max1 < c) {
        max2 = max1;
        max1 = c;
      }
      else if(max2 < c) max2 = c;
      if(b != max2) {
        cnt++;
      }
    }
    a = b; b = c;
  }
  cout << cnt << endl;
  return 0;
}