#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using llu = long long unsigned;

vector<ll> dx = { 0, 0, -1, 1};
vector<ll> dy = {-1, 1,  0, 0};

#define MOD 1000000007
int main() {
    int N;
    cin >> N;
    vector<int> A(N);
    for (int i=0; i<N; i++) { cin >> A[i]; }
    int ret = 0;
    for (int i=0; i<N-2; i++) {
        int maxV = max({A[i], A[i+1], A[i+2]});
        int minV = min({A[i], A[i+1], A[i+2]});
        if (A[i+1] == maxV || A[i+1] == minV) { ret++; }
    }
    cout << ret << endl;
    return 0;
}