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 5.4.1) (judge verdict: Accepted)

// https://atcoder.jp/contests/abc132/tasks/abc132_b

#include <stdio.h>
#define forn(i,L,R) for (int i = L; i < R; i++)
#define wez(n) int (n); scanf("%d",&(n))
#define getInt(a) scanf("%d", &a)

int main(){
    wez(n);
    int arr[20], cnt = 0;
    forn(i, 0, n)
        getInt(arr[i]);
    forn(i, 1, n - 1)
        if ((arr[i - 1] > arr[i] && arr[i + 1] < arr[i]) || (arr[i - 1] < arr[i] && arr[i + 1] > arr[i]))
            cnt++;
            
    printf("%d\n", cnt);
}