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#include<bits/stdc++.h>
#define st first
#define nd second
#define pb push_back
#define mp(a, b) make_pair(a, b)
#define all(x) (x).begin(), (x).end()
#define rev(x) reverse(all(x))
#define sor(x) sort(all(x))
#define sz(x) (int)(x).size()
#define rsz(x) resize(x)
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
typedef vector<pii > vii;
typedef vector<ll> vl;
typedef vector<pll> vll;
typedef string str;
#define BOOST ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);

const int MN = 5e4 + 5LL;
int tab[MN];
int tab2[MN];
const int inf = 1e9;

int main()
{
    BOOST;
    int n;
    cin>>n;
    for(int i = 0; i < n; i++)
    {
        int a;
        cin>>a;
        tab[i] = a;
        tab2[i] = a;
    }
    int res = 0;
    for(int i = 0; i < n-1; i++)
    {
        if(i&1)
        {
            if(tab[i] <= tab[i+1])
            {
                tab[i+1] = -inf;
                res++;
            }
        }
        else
        {
            if(tab[i] >= tab[i+1])
            {
                tab[i+1] = inf;
                res++;
            }
        }
    }
    int mini = res;
    res = 0;
    for(int i = 0; i < n-1; i++)
    {
        if(i&1)
        {
            if(tab2[i] >= tab2[i+1])
            {
                tab2[i+1] = inf;
                res++;
            }
        }
        else
        {
            if(tab2[i] <= tab2[i+1])
            {
                tab2[i+1] = -inf;
                res++;
            }
        }
    }
    mini = min(mini,res);
    cout<<mini;
    return 0;
}