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

const int Inf = 1e9;

int main()
{
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n;
  cin>>n;
  vector<int>Ar;
  for(int i=0;i<n;i++)
  {
    int x;
    cin>>x;
    Ar.push_back(x);
  }
  vector<int>Tmp = Ar;
  int w = 0, W = Inf;
  for(int i=1;i<n;i+=2)
  {
    if(Tmp[i] >= Tmp[i-1] || (i != n-1 && Tmp[i] >= Tmp[i+1]))
      Tmp[i] = -Inf, w++;
  }
  W = min(w, W), w = 0, Tmp = Ar;
  for(int i=1;i<n;i++)
  {
    if(Tmp[i] <= Tmp[i-1] || (i != n-1 && Tmp[i] <= Tmp[i+1]))
      Tmp[i] = Inf, w++;
  }
  W = min(w,W);
  cout<<W;
}