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 C (GCC 9.2.1) (judge verdict: Accepted)

#include<stdio.h>
int main( )
{
    int n , num[1000] , count = 0  , i ;
    scanf("%d" , &n);
    
    for( i = 1 ; i <= n ; i++)
        scanf("%d" , &num[i]);
    
    for( i = 1 ; i < n-1 ; i++)
    {
        if( num[i] < num[i+1])
        {
            if( num[i+1] < num[i+2])
                count++ ;
        }
        
        else if( num[i] > num[i+1] )
        {
                if( num[i+1] > num[i+2])    
                    count++ ;
        }
    }
    
    printf("%d\n" , count);
    
    return 0 ;
}