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#include <bits/stdc++.h>
using namespace std;

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int n;
  cin >> n;
  vector<int> v(n);
  vector<int> w(n);
  for (int i = 0; i < n; i++) {
    cin >> v[i];
    w[i] = v[i];
  }

  // gora dol gora
  int a = 0;
  bool a_ok = true;
  bool up_down = true;
  for (int i = 1; i < n; i++) {
    if (up_down) {
      if (v[i - 1] <= v[i]) {
        if (v[i] == -1000000000) {
          a_ok = false;
          break;
        }
        v[i] = -1000000000;
        a++;
      }
    } else {
      if (v[i - 1] >= v[i]) {
        if (v[i] == 1000000000) {
          a_ok = false;
          break;
        }
        v[i] = 1000000000;
        a++;
      }
    }

    up_down = !up_down;
  }

  // dol gora dol
  int b = 0;
  bool b_ok = true;
  up_down = false;
  for (int i = 1; i < n; i++) {
    if (up_down) {
      if (w[i - 1] <= w[i]) {
        if (w[i] == -1000000000) {
          b_ok = false;
          break;
        }
        w[i] = -1000000000;
        b++;
      }
    } else {
      if (w[i - 1] >= w[i]) {
        if (w[i] == 1000000000) {
          b_ok = false;
          break;
        }
        w[i] = 1000000000;
        b++;
      }
    }

    up_down = !up_down;
  }

  if (a_ok && b_ok)
    cout << min(a, b);
  else if (a_ok)
    cout << a;
  else
    cout << b;
}