#include <bits/stdc++.h>
using namespace std;
using ll = long long;
constexpr int INF = (int)1e9 + 1001010;
constexpr ll llINF = (ll)4e18 + 22000020;
const string endn = "\n";
template <class T> inline auto vector2(size_t i, size_t j, const T &init = T()) {return vector(i, vector<T>(j, init));}
const string ELEM_SEPARATION = " ", VEC_SEPARATION = endn;
template<class T> istream& operator >>(istream &i, vector<T> &A) {for(auto &I : A) {i >> I;} return i;}
template<class T> ostream& operator <<(ostream &o, const vector<T> &A) {int i=A.size(); for(auto &I : A){o << I << (--i ? ELEM_SEPARATION : "");} return o;}
template<class T> ostream& operator <<(ostream &o, const vector<vector<T>> &A) {int i=A.size(); for(auto &I : A){o << I << (--i ? VEC_SEPARATION : "");} return o;}
template<class T> vector<T>& operator ++(vector<T> &A, int n) {for(auto &I : A) {I++;} return A;}
template<class T> vector<T>& operator --(vector<T> &A, int n) {for(auto &I : A) {I--;} return A;}
template<class T, class U> bool chmax(T &a, const U &b) {return ((a < b) ? (a = b, true) : false);}
template<class T, class U> bool chmin(T &a, const U &b) {return ((a > b) ? (a = b, true) : false);}
ll floor(ll a, ll b){if(b < 0) a = -a, b = -b; return a >= 0 ? a/b : (a+1)/b - 1;}
ll ceil (ll a, ll b){if(b < 0) a = -a, b = -b; return a > 0 ? (a-1)/b + 1 : a/b;}
ll bit(unsigned long long val, unsigned long long digit){return (val >> digit) & 1;}
// ================================== ここまでテンプレ ==================================


int main(int argc, char *argv[]){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int n; cin >> n;
    vector<int> a(n); cin >> a;
    ll ans = 0;
    for(int i = 0; i < n-2; i++){
        int j = i + 1;
        int k = i + 2;
        set<int> st = {a[i], a[j], a[k]};
        if(st.size() != 3) continue;
        int second = *next(st.begin(), 1);
        if(a[i] == second || a[k] == second) ans++;
    }

    cout << ans << endl;
    return 0;
}