#include <algorithm>
#include <iostream>
#include <iomanip>
#include <limits.h>
#include <map>
#include <math.h>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <string>
#include <utility>
#include <vector>
#include <stack>

using namespace std;
#define rep(i, n) for (int i = 0; i < n; i++)
#define rep1(i, n) for (int i = 1; i < n + 1; i++)
#define all(A) A.begin(), A.end()
#define itr(A, l, r) A.begin() + l, A.begin() + r
#define debug(var) cout << #var << " = " << var << endl;
typedef long long ll;

template <typename T>
struct Compress
{
    vector<T> xs;

    Compress() = default;

    Compress(const vector<T> &vs)
    {
        add(vs);
    }

    Compress(const initializer_list<vector<T>> &vs)
    {
        for (auto &p : vs)
            add(p);
    }

    void add(const vector<T> &vs)
    {
        copy(begin(vs), end(vs), back_inserter(xs));
    }

    void add(const T &x)
    {
        xs.emplace_back(x);
    }

    void build()
    {
        sort(begin(xs), end(xs));
        xs.erase(unique(begin(xs), end(xs)), end(xs));
    }

    vector<int> get(const vector<T> &vs) const
    {
        vector<int> ret;
        transform(begin(vs), end(vs), back_inserter(ret), [&](const T &x)
                  { return lower_bound(begin(xs), end(xs), x) - begin(xs); });
        return ret;
    }

    int get(const T &x) const
    {
        return lower_bound(begin(xs), end(xs), x) - begin(xs);
    }

    const T &operator[](int k) const
    {
        return xs[k];
    }
};

int main(void)
{
    int n;
    cin >> n;
    vector<int> a(n);
    rep(i, n)
    {
        cin >> a[i];
    }
    int ans = 0;
    rep(i, n - 2)
    {
        vector<int> tmp;
        rep(j, 3)
        {
            tmp.push_back(a[i + j]);
        }
        auto print_vector = [](auto v)
        {
            for (auto i : v)
            {
                cout << i << ',';
            }
            cout << endl;
        };
        // print_vector(tmp);
        Compress<int> comp(tmp);
        comp.build();
        vector<int> z = comp.get(tmp);
        // print_vector(z);
        if (*max_element(all(z)) < 2)
        {
            continue;
        }
        if (z[0] == 1 || z[2] == 1)
        {
            ans++;
        }
    }
    cout << ans << endl;
}