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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
using namespace std;
using i64 = int64_t;
#define rep(i,n) for(int i=0;i<n;++i)
#define rep2(i,x,n) for(int i=x;i<n;++i)

int main()
{
    int n;
    cin >> n;
    vector<int> p(n);
    rep(i,n) cin >> p[i];

    int cnt = 0;
    rep2(i,1,n-1)
    {
        if(p[i-1]<p[i] && p[i]<p[i+1]) cnt++;
        else if(p[i-1]>p[i] && p[i]>p[i+1]) cnt++;
    }        

    cout << cnt << endl;
    return 0;
}