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

const int duzo = 50007;
int tab[duzo];
int tab1[duzo];
int tab2[duzo];

int main(){
    cin.tie(0); cout.tie(0); ios_base::sync_with_stdio(0);
    int n;
    cin >> n;
    for (int i = 0; i < n; i++){
        cin >> tab[i];
        tab1[i] = tab[i];
        tab2[i] = tab[i];
    }

    //duze male duze
    //  0    1    2
    int wynik1=0;
    for (int i = 1; i < n; i++){
        if (i%2==0 and tab1[i] <= tab1[i-1]){
            wynik1++;
            tab1[i]=1000000007;
        }
        else if (i%2==1 and tab1[i] >= tab1[i-1]){
            wynik1++;
            tab1[i]=-1000000007;
        }
    }


    //male duze male
    //  0    1    2


    int wynik2=0;
    for (int i = 1; i < n; i++){
        if (i%2==0 and tab2[i] >= tab2[i-1]){
            wynik2++;
            tab2[i]=-1000000007;
        }
        else if (i%2==1 and tab2[i] <= tab2[i-1]){
            wynik2++;
            tab2[i]=1000000007;
        }
    }

    cout << min(wynik1, wynik2);




    //male duze male
}