//sept 17,2020
#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#include <bits/stdc++.h>
using namespace std;
#define int                     long long   
#define double                  long double
#define endl                    "\n"
#define pb                      push_back
#define PI                      3.1415926535897932384626433832795l
#define F                       first
#define S                       second
#define mp                      make_pair
#define f(i,n)                  for(int i=0;i<n;i++)
#define loop(i,a,b)             for(int i=a;i<b;i++)        
#define fastio                  ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define all(v)                  (v).begin(),(v).end()
#define rall(v)                 (v).rbegin(),(v).rend()
#define gcd(a,b)                __gcd((a),(b))
#define fill(a,value)           memset(a,value,sizeof(a));
#define minn(v)                 *min_element(v.begin(), v.end());
#define maxx(v)                 *max_element(v.begin(), v.end());
#define print(x)                cout<<(x)<<endl;
#define sum(v)+x                accumulate(v.begin(), v.end(),x);
#define debug(x)                cout<<#x<<'='<<(x)<<endl;
typedef pair<int,int>           pii;
typedef vector<int>             vi;
const int mod=1e9+7; 
const int MOD=2019;

//to check if a no is prime or not?
bool isPrime(int n) 
{ 
    if (n <= 1) 
        return false; 
    if (n <= 3) 
        return true; 
    if (n % 2 == 0 || n % 3 == 0) 
        return false; 
  
    for (int i = 5; i * i <= n; i = i + 6) 
        if (n % i == 0 || n % (i + 2) == 0) 
            return false; 
  
    return true; 
}
// minimum subaaray sum of size k-sliding window approach
int findSubarray(int arr[], int n, int k)
{   
	int window_sum = 0;
	int min_window = INT_MAX;
	int last = 0;
	for (int i = 0; i < n; i++)
	{
		window_sum += arr[i];
		if (i + 1 >= k)
		{
			if (min_window > window_sum)
			{
				min_window = window_sum;
				last = i;
			}
			window_sum -= arr[i + 1 - k];
		}
	}
	int sum=0;
	for(int i=last-k+1;i<=last;i++)
	{
	    sum+=arr[i];
	}
	return sum;
}
//finds the next permutation to given sequence of nos
int nextpermutation(vi v)
{
    vi t=v;
    sort(all(t));
    int x=0;
    while(true)
    {
        x++;
        if(t==v)
        {
            return x;
        }
        next_permutation(all(t));
    }
}
vector<int>factors(int n) 
{ 
    // Note that this loop runs till square root 
    vi ans;
    for (int i=1; i<=sqrt(n); i++) 
    { 
        if (n%i == 0) 
        { 
            if (n == i*i )ans.pb(i);
            else
            {
                ans.pb(i);
                if (i!=n/i)ans.pb(n/i);
            }
        } 
    }
    sort(all(ans));
    return ans;
}
 
// Recursive C++ program to check if a string is subsequence of another string 
bool isSubSequence(char str1[], char str2[], int m, int n) 
{ 
    // Base Cases 
    if (m == 0) return true; 
    if (n == 0) return false; 
  
    // If last characters of two strings are matching 
    if (str1[m-1] == str2[n-1]) 
        return isSubSequence(str1, str2, m-1, n-1); 
  
    // If last characters are not matching 
    return isSubSequence(str1, str2, m, n-1); 
} 
void findDivisors(int n) 
{ 
  
    int div[n + 1]; 
    memset(div, 0, sizeof div); 
    for (int i = 1; i <= n; i++) { 
        for (int j = 1; j * i <= n; j++) 
            div[i * j]++; 
    } 
    int ans=0;
    for (int i = 1; i <= n; i++) 
        ans+= i*div[i];
    cout<<ans<<endl;    
}

int power(int x, int y, int p) 
{ 
    int res = 1; // Initialize result 
  
    x = x % p; // Update x if it is more than or 
    // equal to p 
  
    while (y > 0) { 
        // If y is odd, multiply x with result 
        if (y & 1) 
            res = (res * x) % p; 
  
        // y must be even now 
        y = y >> 1; // y = y/2 
        x = (x * x) % p; 
    } 
    return res; 
} 
  
// Returns n^(-1) mod p 
int modInverse(int n, int p) 
{ 
    return power(n, p - 2, p); 
} 
  
// Returns nCr % p using Fermat's little 
// theorem. 
int nCr(int n,  int r, int p) 
{ 
    // Base case 
    if (r == 0) 
        return 1; 
    int fac[n + 1]; 
    fac[0] = 1; 
    for (int i = 1; i <= n; i++) 
        fac[i] = (fac[i - 1] * i) % p; 
  
    return (fac[n] * modInverse(fac[r], p) % p * modInverse(fac[n - r], p) % p) % p; 
} 
double dist (int x1, int y1, int x2, int y2) {
    double a = (x1 - x2) * (x1 - x2);
    double b = (y1 - y2) * (y1 - y2);
 
    return sqrt(a + b);
}
int maxSubArraySum(vi a, int size) 
{ 
    int max_so_far = INT_MIN, max_ending_here = 0; 
  
    for (int i = 0; i < size; i++) 
    { 
        max_ending_here = max_ending_here + a[i]; 
        if (max_so_far < max_ending_here) 
            max_so_far = max_ending_here; 
  
        if (max_ending_here < 0) 
            max_ending_here = 0; 
    } 
    return max_so_far; 
}
int min_modulo(int l, int r) 
{ 
    if (r - l >= MOD) 
        return 0; 
    else { 
        int ans = MOD - 1; 
        for (int i = l; i <= r; i++) { 
            for (int j = i + 1; j <= r; j++) { 
                ans = min(ans, (i * j) % MOD); 
            } 
        } 
        return ans; 
    } 
}
int digitSum(int n)
{
    int res=0;
    while(n>0)
    {
        res+=n%10;
        n/=10;
    }
    return(res);
}
bool isPerfectSquare(double x) 
{   
  // Find floating point value of  
  // square root of x. 
  double sr = sqrt(x); 
  
  // If square root is an integer 
  return ((sr - floor(sr)) == 0); 
} 
signed main() 
{
    fastio;
    cout << fixed << setprecision(12);
    int T;
    T=1;
    //cin>>T;
    f(tc,T)
    {
        //cout<<"Case "<<tc+1<<":";
        int n;
        cin>>n;
        vi a(n);
        f(i,n)cin>>a[i];
        int ans=0;
        for(int i=1;i<n-1;i++)
        {
            if((a[i]>a[i-1] and a[i]<a[i+1]) or (a[i]>a[i+1] and a[i]<a[i-1]))ans++;
        }
        print(ans)
        
        
    }
    return 0;
}
 


Measured memory_bytes: 3588