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#include <iostream>
    #include <vector>
    using namespace std;
    int minChanges(vector<int> a, bool firstIncreasing) {
      int changes = 0;

      for (int i = 1; i < a.size(); i++) {
      	if (firstIncreasing) {
      		if (i % 2 == 0 && a[i] >= a[i-1]) {
      			a[i] = -1e9;
      			changes++;
      		} else if (i % 2 == 1 && a[i] <= a[i-1]) {
      			a[i] = 1e9;
      			changes++;
      		}
      	} else {
      		if (i % 2 == 0 && a[i] <= a[i-1]) {
      			a[i] = 1e9;
      			changes++;
      		} else if (i % 2 == 1 && a[i] >= a[i-1]) {
      			a[i] = -1e9;
      			changes++;
      		}
      	}
      }
      return changes;
    }

    int main() {
    vector <int> vec;

    int n;

    cin >> n;

    for (int i = 0; i < n; i++) {
        int c;
        cin >> c;
        vec.push_back(c);
        }
      cout << min(minChanges(vec, true), minChanges(vec, false)) << endl;



      return 0;
    }