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#include <iostream>

using namespace std;
int tab[50009];
int tab2[50009];
int solve1(int n)
{
   int wyn = 0;
   for(int i = 1; i < n; i++)
   {
      if(i % 2 == 0)
      {
         if(tab[i] <= tab[i - 1])
         {
            tab[i] = 2000000;
            wyn++;
         }
      }
      else
      {
         if(tab[i] >= tab[i - 1])
         {
            tab[i] = -2000000;
            wyn++;
         }
      }
   }
   return wyn;
}
int solve2(int n)
{
   int wyn = 0;
   for(int i = 1; i < n; i++)
   {
      if(i % 2 == 1)
      {
         if(tab2[i] <= tab2[i - 1])
         {
            tab2[i] = 2000000;
            wyn++;
         }
      }
      else
      {
         if(tab2[i] >= tab2[i - 1])
         {
            tab2[i] = -2000000;
            wyn++;
         }
      }
   }
   return wyn;
}
int main()
{
   int n;
   cin >> n;
   for(int i = 0; i < n; i++)
   {
      cin >> tab[i];
      tab2[i] = tab[i];
   }
   cout << min(solve1(n), solve2(n));
}