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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(NULL);
    cout.tie(NULL);
    int n;
    cin>>n;
    int a[n];
    int b[n], c[n];
    int B=0, C=0;
    for(int i=0;i<n;i++)
    {
        cin>>a[i];
        b[i]=a[i];
        c[i]=a[i];
    }
    for(int i=1;i<n;i++)
    {
        if(i%2 == 0)
        {
            if(b[i]<=b[i-1])
            {
                b[i]=inf;
                B++;
            }
        }
        else
        {
            if(b[i]>=b[i-1])
            {
                b[i]=-inf;
                B++;
            }
        }
    }
    for(int i=1;i<n;i++)
    {
        if(i%2 == 0)
        {
            if(c[i]>=c[i-1])
            {
                c[i]=-inf;
                C++;
            }
        }
        else
        {
            if(c[i]<=c[i-1])
            {
                c[i]=inf;
                C++;
            }
        }
    }
    cout<<min(B,C)<<"\n";
}