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#include <iostream>
using namespace std;

int n, tmp;
int results_lf[50000];
int results_hf[50000];
int change_lf=0;
int change_hf=0;
int min_value=-2000000;
int max_value=2000000;

int main(){
  cin >> n;
  for(int i=0; i<n; i++){
    cin >> tmp;
    results_lf[i] = tmp;
    results_hf[i] = tmp;
  }
// Assuming that the pattern is lower-higher-lower-...
  for(int i=1; i<n; i++){
    if((i%2==1) and (results_lf[i-1]>=results_lf[i])){
      results_lf[i] = max_value;
      change_lf++;
    }
    if((i%2==0) and (results_lf[i-1]<=results_lf[i])){
      results_lf[i] = min_value;
      change_lf++;
    }
  }
// Assuming that the pattern is higher-lower-higher...
  for(int i=1; i<n; i++){
    if((i%2==0) and (results_hf[i-1]>=results_hf[i])){
      results_hf[i] = max_value;
      change_hf++;
    }
    if((i%2==1) and (results_hf[i-1]<=results_hf[i])){
      results_hf[i] = min_value;
      change_hf++;
    }
  }
  int result =  min(change_hf, change_lf);
  cout << result << endl;
}