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#include <iostream>
#include <vector>

int calculate(std::vector<int> & v, bool kind, int n) {
  int max = 1e9, min = -1e9, res = 0;

  for (int i = 1; i < n; i++) {
    if ((v[i] - v[i - 1] >= 0) && (i % 2 == kind)) {
      v[i] = min;
      min ++;
      res ++;
    }
    else if ((v[i] - v[i - 1] <= 0) && (i % 2 == (!kind))) {
      v[i] = max;
      max --;
      res ++;
    }
  }
  return res;
}

int main() {
  std::ios_base::sync_with_stdio(false);
  std::cin.tie(NULL);
  std::cout.tie(NULL);

  int n;
  std::cin >> n;

  std::vector<int> v1(n), v2(n);

  for (int i = 0; i < n; i++) {
    std::cin >> v1[i];
    v2[i] = v1[i];
  }

  int res = std::min(calculate(v1, true, n), calculate(v2, false, n));
  std::cout << res << "\n";
}