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#include <iostream>
#include <bits/stdc++.h>

using namespace std;

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

    int n;
    cin >> n;
    vector<int> tab = vector<int>(n, 0);
    for(int i = 0 ; i < n ; ++i) cin >> tab[i];
    int plus = 0;
    int minus = 0;
    int w = 2*n;

    for(int i = 1 ; i < n ; i+=2)
    {
        if(tab[i-1] >= tab[i] || (i<n-1 && tab[i] <= tab[i+1])) plus++;
        if(tab[i-1] <= tab[i] || (i<n-1 && tab[i] >= tab[i+1])) minus++;
    }
    w = min(plus, minus);
    plus = 0;
    minus = 0;

    for(int i = 0 ; i < n ; i+=2)
    {
        if((i>0 && tab[i-1] >= tab[i]) || (i<n-1 && tab[i] <= tab[i+1])) plus++;
        if((i>0 && tab[i-1] <= tab[i]) || (i<n-1 && tab[i] >= tab[i+1])) minus++;
    }
    
    w = min(w, minus);
    w = min(w, plus);

    cout << w;

    return 0;
}