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//Wojciech Rybak Zbigniew100noga
#include <bits/stdc++.h>
using namespace std;

#define int long long
#define ll long long
#define pb push_back
#define nd second
#define st first
#define sz size
#define forr(i, n) for(int i=1;i<=n;i++)
const ll infl=1e18+90;
const int inf=1e9+90;
const int roz=1e5;

int tab[roz], tab2[roz];

signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int n, wyn1=0, wyn2=0;
    cin>>n;
    for(int i=1;i<=n;i++)
    {
        cin>>tab[i];
        tab2[i]=tab[i];
    }
    for(int i=2;i<=n;i++)
    {
        //cerr<<"dla i = "<<i<<" wyn1 = "<<wyn1<<" wyn2 = "<<wyn2<<"\n";
        if(i%2==0)
        {
            if(tab[i]<=tab[i-1])
            {
                tab[i]=inf;
                wyn1++;
            }
            if(tab2[i]>=tab2[i-1])
            {
                tab2[i]=-inf;
                wyn2++;
            }
        }
        else
        {
            if(tab2[i]<=tab2[i-1])
            {
                tab2[i]=inf;
                wyn2++;
            }
            if(tab[i]>=tab[i-1])
            {
                tab[i]=-inf;
                wyn1++;
            }
        }
    }
    //cerr<<wyn1<<" "<<wyn2<<"\n";
    cout<<min(wyn1, wyn2)<<"\n";
}