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#include<iostream>
#include<cstdio>
#include<vector>

using namespace std;
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int n;
    cin >> n;
    vector<int> tab, tab1, tab2;
    int a;
    for (int i = 0; i < n; i++)
    {
        cin >> a;
        tab.push_back(a);
        tab1.push_back(a);
        tab2.push_back(a);
    }
    int odp1 = 0;
    int odp2 = 0;
    for (int i = 0; i < n - 1; i++)
    {
        if (i % 2 == 0)
        {
            if (tab1[i + 1] >= tab1[i])
            {
                if (tab[i] != tab1[i])
                {
                    if (tab1[i + 1] < 1000000)
                    {
                        tab1[i] = tab1[i + 1] + 1;
                        continue;
                    }
                }
                if (tab1[i] > -1000000)
                {
                    tab1[i + 1] = tab1[i] - 1;
                    odp1++;
                    continue;
                }
                tab1[i] = tab1[i + 1] + 1;
                odp1++;
            }
        }
        else
        {
            if (tab1[i + 1] <= tab1[i])
            {
                if (tab[i] != tab1[i])
                {
                    if (tab1[i + 1] > -1000000)
                    {
                        tab1[i] = tab1[i + 1] - 1;
                        continue;
                    }
                }
                if (tab1[i] < 1000000)
                {
                    tab1[i + 1] = tab1[i] + 1;
                    odp1++;
                    continue;
                }
                tab1[i] = tab1[i + 1] - 1;
                odp1++;
            }
        }
        if (i % 2 == 1)
        {
            if (tab2[i + 1] >= tab2[i])
            {
                if (tab[i] != tab2[i])
                {
                    if (tab2[i + 1] < 1000000)
                    {
                        tab2[i] = tab2[i + 1] + 1;
                        continue;
                    }
                }
                if (tab2[i] > -1000000)
                {
                    tab2[i + 1] = tab2[i] - 1;
                    odp2++;
                    continue;
                }
                tab2[i] = tab2[i + 1] + 1;
                odp2++;
            }
        }
        else
        {
            if (tab2[i + 1] <= tab2[i])
            {
                if (tab[i] != tab2[i])
                {
                    if (tab2[i + 1] > -1000000)
                    {
                        tab2[i] = tab2[i + 1] - 1;
                        continue;
                    }
                }
                if (tab2[i] < 1000000)
                {
                    tab2[i + 1] = tab2[i] + 1;
                    odp2++;
                    continue;
                }
                tab2[i] = tab2[i + 1] - 1;
                odp2++;
            }
        }
    }
    if (odp1 < odp2)
    {
        cout << odp1;
    }
    else
    {
        cout << odp2;
    }
    return 0;
}