#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <queue>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;

static const double EPS = 1e-8;
static const double PI = 4.0 * atan(1.0);
static const double PI2 = 8.0 * atan(1.0);

#define REP(i,n)	for(int i=0;i<(int)n;++i)
#define ALL(c)		(c).begin(),(c).end()
#define CLEAR(v)	memset(v,0,sizeof(v))
#define MP(a,b)		make_pair((a),(b))
#define ABS(a)		((a)>0?(a):-(a))
#define FOR(i,s,n)	for(int i=s;i<(int)n;++i)

int main(int argc, char **argv) {
	int N, A[100], t[3];
	cin >> N;
	REP(i, N) cin >> A[i];
	int res = 0;
	REP(i, N - 2) {
		REP(j, 3) t[j] = A[i + j];
		sort(t, t + 3);
		if (t[0] == t[1] || t[1] == t[2]) continue;
		if (A[i] == t[1] || A[i + 2] == t[1]) ++res;
	}
	cout << res << endl;
	return 0;
}