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#include<bits/stdc++.h>
using namespace std;
int tab[50010];
int tab2[50010];
int main()
{
    int n;
    cin>>n;
    for(int i=0;i<n;i++){
        cin>>tab[i];
        tab2[i]=tab[i];
    }
    int wyn1=0,wyn2=0;
    if(n%2==0)tab[n]=1e9+7;
    for(int i=1;i<n;i+=2){

        if(tab[i]>=tab[i-1]){
            tab[i]=-1e9;
            wyn1++;
        }
        if(tab[i]>=tab[i+1]){
            tab[i+1]=1e9;
            wyn1++;
        }
        //cout<<tab[i-1]<<" "<<tab[i]<<" ";
    }
    //cout<<"\n"<<wyn1<<"\n";
    if(n%2==0)tab2[n]=-1e9-7;
    for(int i=1;i<n;i+=2){

        if(tab2[i]<=tab2[i-1]){
            tab2[i]=1e9;
            wyn2++;
        }
        if(tab2[i]<=tab2[i+1]){
            tab2[i+1]=-1e9;
            wyn2++;
        }
        //cout<<tab2[i-1]<<" "<<tab2[i]<<" ";
    }
    cout<<min(wyn1,wyn2)<<"\n";
    return 0;


}