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#include <iostream>
#include <utility>

using namespace std;

constexpr int S = 5e5 + 5, x = 1e9;

int w1 = 0, w2 = 0, w3 = 1, w4 = 1;
int n;
int tab1[S];
int tab2[S];
int tab3[S];
int tab4[S];

int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    cin >> n;
    for(int i = 0; i < n; i++)
    {
        cin >> tab1[i];
        tab4[i] = tab3[i] = tab2[i] = tab1[i];
    }
    tab3[0] = x;
    tab4[0] = -x;
    for(int i = 1; i < n; i++)
    {
        if(i & 1)
        {
            if(tab1[i] >= tab1[i - 1])
            {
                tab1[i] = -x;
                w1++;
            }
        }
        else
        {
            if(tab1[i] <= tab1[i - 1])
            {
                tab1[i] = x;
                w1++;
            }
        }
        if(tab1[i] == tab1[i  -1])
        {
            w1 = 999999;
            break;
        }
    }
    for(int i = 1; i < n; i++)
    {
        if(!(i & 1))
        {
            if(tab2[i] >= tab2[i - 1])
            {
                tab2[i] = -x;
                w2++;
            }
        }
        else
        {
            if(tab2[i] <= tab2[i - 1])
            {
                tab2[i] = x;
                w2++;
            }
        }
        if(tab2[i] == tab2[i  -1])
        {
            w2 = 999999;
            break;
        }
    }
    for(int i = 1; i < n; i++)
    {
        if(i & 1)
        {
            if(tab3[i] >= tab3[i - 1])
            {
                tab3[i] = -x;
                w3++;
            }
        }
        else
        {
            if(tab3[i] <= tab3[i - 1])
            {
                tab3[i] = x;
                w3++;
            }
        }
        if(tab3[i] == tab3[i  -1])
        {
            w3 = 999999;
            break;
        }
    }
    for(int i = 1; i < n; i++)
    {
        if(!(i & 1))
        {
            if(tab4[i] >= tab4[i - 1])
            {
                tab4[i] = -x;
                w4++;
            }
        }
        else
        {
            if(tab4[i] <= tab4[i - 1])
            {
                tab4[i] = x;
                w4++;
            }
        }
        if(tab4[i] == tab4[i  -1])
        {
            w4 = 999999;
            break;
        }
    }
    cout << min(min(w1, w2), min(w3, w4));
    return 0;
}