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 Python (3.4.3) (judge verdict: Wrong Answer)

import sys
from sys import stdin
import numpy as np

def main():
    #pass
    n = int(stdin.readline().rstrip())
    p = np.array(stdin.readline().rstrip().rsplit())
    #print(n,p_list,type(p_list))
    count=0
    for i in range(n-2):
        #p_list[i+1] p_2
        if p[i+2]<p[i+1]<p[i] or p[i+2]>p[i+1]>p[i]:
            count+=1
    print(count)
    return

if __name__ == "__main__":
    main()