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#include <iostream>
#include <vector>
using namespace std;

int main() {

  int n;
  scanf("%d", &n);

  int ans1 = 0, ans2 = 0;

  vector<int> tone(n+5);

  for(int i = 1; i <= n; i++) {
    scanf("%d", &tone[i]);
  }

  //opcja 1 - poczatek to gora

  int counter = 0;

  tone[0] = tone[1] - 1;

  if(n % 2 == 0) {
    tone[n+1] = tone[n] + 1;
  } else {
    tone[n+1] = tone[n] - 1;
  }

  for(int i = 1; i <= n; i++) {
    if(i % 2 == 1) {
      if(tone[i] <= tone[i+1]) {
        counter++;
        if(counter % 2 == 1) {
            ans1++;
        }
      } else {
        counter = 0;
      }
    } else {

      if(tone[i] >= tone[i+1]) {
        counter++;
        if(counter % 2 == 1) {
            ans1++;
        }
      } else {
        counter = 0;
      }
    }


  }

  counter = 0;


  //opcja 2

  tone[0] = tone[1] + 1;

  if(n % 2 == 0) {
    tone[n+1] = tone[n] - 1;
  } else {
    tone[n+1] = tone[n] + 1;
  }


  for(int i = 1; i <= n; i++) {
    if(i % 2 == 1) {
      if(tone[i] >= tone[i+1]) {
        counter++;
        if(counter % 2 == 1) {
            ans2++;
        }
      } else {

        counter = 0;

      }

    } else {

      if(tone[i] <= tone[i+1]) {
        counter++;
        if(counter % 2 == 1) {
            ans2++;
        }
      } else {

        counter = 0;

      }
    }
  }


  ans1 = min(ans1, ans2);

  printf("%d", ans1);


 return 0;
}