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>
#include <iostream>
#include <vector>
#include <string>
#include <numeric>
#include <iostream>
#include <cmath>
#include <algorithm>
#include <iomanip>
#include <queue>

#define rep(i,n) for(int i=0;i<n;i++)
using namespace std;
typedef long long ll;

int main() {
	int N;
	cin >> N;
	vector<int> p(N);
	rep(i, N) {
		cin >> p[i];
	}
	
	int dif = 0;
	int dif_old = 0;
	int cnt = 0;
	rep(i, N-1) {
		if(p[i]<p[i+1]) dif = 1;
		else dif = -1;

		if(dif==dif_old) cnt++;

		dif_old = dif;
	}

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