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#include <bits/stdc++.h>

using namespace std;

int main() {
  int n;
  cin >> n;
  vector<int> a(n);
  for (int& i : a) cin >> i;
  vector<int> b = a;
  int ans1 = 0;
  for (int i = 0; i < n-1; i++) {
    if (i % 2) {
      if (a[i] <= a[i+1]) { a[i+1] = -1e8; ans1++; }
    }
    else {
      if (a[i] >= a[i+1]) { a[i+1] = 1e8; ans1++; }
    }
  }
  int ans2 = 0;
  a = b;
  for (int i = 0; i < n-1; i++) {
    if (i % 2) {
      if (a[i] >= a[i+1]) { a[i+1] = 1e8; ans2++; }
    }
    else {
      if (a[i] <= a[i+1]) { a[i+1] = -1e8; ans2++; }
    }
  }

  cout << min(ans1, ans2) << '\n';

  return 0;
}