Problem:
Score : 200 points

Problem Statement

We have a permutation p = {p_1,\ p_2,\ ...,\ p_n} of {1,\ 2,\ ...,\ n}.

Print the number of elements p_i (1 < i < n) that satisfy the following condition:

p_i is the second smallest number among the three numbers p_{i - 1}, p_i, and p_{i + 1}.

Constraints

All values in input are integers.

3 \leq n \leq 20

p is a permutation of {1,\ 2,\ ...,\ n}.

Input

Input is given from Standard Input in the following format:

n
p_1 p_2 ... p_n

Output

Print the number of elements p_i (1 < i < n) that satisfy the condition.

Sample Input 1

5
1 3 5 4 2

Sample Output 1

2

p_2 = 3 is the second smallest number among p_1 = 1, p_2 = 3, and p_3 = 5. Also, p_4 = 4 is the second smallest number among p_3 = 5, p_4 = 4, and p_5 = 2. These two elements satisfy the condition.

Sample Input 2

9
9 6 3 2 5 8 7 4 1

Sample Output 2

5

Solution in PyPy3 (2.4.0) (judge verdict: Accepted)

#B

n = int(input())
p = [int(x) for x in input().split()]

#n, *p = [int(x) for x in Input.split()]

a = ["#",p[0],p[1]]
count = 0

for i in range(2,n):
    a.pop(0)
    a.append(p[i])
    
    if (a[1]<a[0] and a[1]>a[2])or(a[1]>a[0] and a[1]<a[2]):
        count+=1
    
    #print(a)

print(count)