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#include <bits/stdc++.h>
using namespace std;

const int inf = 1000000005;
const int fni = -1000000005;
int a[50005];
int a2[50005];

int main(){
  ios_base::sync_with_stdio(0); cin.tie(0);
  
  int n,wyn1=0,wyn2 =0;
  cin>>n;
  for(int i=0; i<n; i++)
  {
    cin>>a[i];
    a2[i] = a[i];
  }
    
  for(int i=0; i<n-1; i++)
  {
    if(i&1)
    {
      if(a[i+1]>=a[i])
      {
        wyn1++;
        a[i+1] = fni;
      }
    }
    else
    {
      if(a[i+1]<=a[i])
      {
        wyn1++;
        a[i+1] = inf;
      }
    }
  }
  for(int i=0; i<n-1; i++)
  {
    if(i&1)
    {
      if(a2[i+1]<=a2[i])
      {
        wyn2++;
        a2[i+1] = inf;
      }
    }
    else
    {
      if(a2[i+1]>=a2[i])
      {
        wyn2++;
        a2[i+1] = fni;
      }
    }
  }
  cout<<min(wyn1,wyn2); 
}