11496 - Musical Loop.cpp

/*input

*/

#include <stdio.h>
#include <cmath>
#include <set> 
#include <vector>
#include <iostream>
#include <algorithm>
#include <sstream>
#include <string.h>
#include <stack>
#include <map>
#include <cstring>
#include <algorithm>
#include <iomanip>
#include <queue>
#include <functional>

using namespace std;

#define r(input) freopen("input.txt","r",stdin)
#define w(output) freopen("output.txt","w",stdout)

#define FOR(i, a) for ( int i = 0 ; i < a ; i++ )
#define FOREACH(l) for (auto it = l.begin(); it != l.end(); it++)

#define BitCount(i) __builtin_popcount(i)
#define Sort(v) sort(v.begin(),v.end())
#define cover(a, d) memset(a,d,sizeof(a))
#define remove(v,e) v.erase(std::find(v.begin(),v.end(),e))
#define is_in(container, element) (container.find(element) != container.end())

#define sz size
#define pb push_back
#define mp make_pair
#define ft first
#define sd second

#define VISITED 1
#define UNVISITED 0
#define INF 1000000000

typedef long long ll;
typedef pair<int,int> ii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef pair<int,ii> triple;

inline int toint(string s){ll v; istringstream sin(s);sin>>v;return v;}
inline ll toll(string s){ll v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) { ostringstream sout; sout << x; return sout.str();}

class Compare
{
public:
	bool operator() (ii t1 , ii t2){
		return t1>t2;
	}
	
};

int arr[20000];

int main()
{
	int n;
	while ( cin >> n)
	{
		if ( !n ) break;
		cover(arr, 0);
		FOR(i , n) cin >> arr[i];
		int cnt = 0;

		for ( int i = 0 ; i < n  ; i++)
		{
			int j = (i + 1) % n;
			int k = (i + 2) % n;
			if (arr[j] < arr[i] && arr[j] < arr[k] || arr[j] > arr[i] && arr[j] > arr[k])
				cnt++;
		} 	
		cout << cnt << endl;

	}
}