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

const int N = 5e4 + 5;
//const int R = 5e5 + 5;

int tab[N];

int n;

int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    cin >> n;

    for(int i = 1; i <= n; i++){
        cin >> tab[i];
    }

    bool dod = 0;
    int sum1 = 0, sum2 = 0;
    for(int i = 2; i <= n; i++){
        if(dod){
            dod = 0;
            continue;
        }

        if(i % 2 == 1 && tab[i] >= tab[i - 1]){
            dod = 1;
            sum1++;
        }

        else if(i % 2 == 0 && tab[i] <= tab[i - 1]){
            dod = 1;
            sum1++;
        }
    }

    dod = 0;
    for(int i = 2; i <= n; i++){
        if(dod){
            dod = 0;
            continue;
        }

        if(i % 2 == 1 && tab[i] <= tab[i - 1]){
            dod = 1;
            sum2++;
        }

        else if(i % 2 == 0 && tab[i] >= tab[i - 1]){
            dod = 1;
            sum2++;
        }
    }

    cout << min(sum1, sum2) << "\n";
    
}