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

typedef long long int LL;

const int MAX_N = 50005;
const int INF = 1000000000;

int n, a;

bool correctDir(const int x, const int y, const int expDir)
{
    return (x < y && expDir == 1) || (x > y && expDir == -1);
}

int newNum(const int expDir)
{
    return expDir * INF;
}

int countNeededChanges(vector<int> elems, int expDir)
{
    int res = 0;

    for(int i = 1; i < n; ++i)
    {
        const bool dirCorrect = correctDir(elems[i-1], elems[i], expDir);

        if(!dirCorrect)
        {
            elems[i] = newNum(expDir);
            ++res;
        }

        expDir *= (-1);
    }

    return res;
}

int main()
{
    ios_base::sync_with_stdio(0);

    cin >> n;
    vector<int> elems;

    for(int i = 0; i < n; ++i)
    {
        cin >> a;
        elems.push_back(a);
    }

    const int res1 = countNeededChanges(elems, 1);
    const int res2 = countNeededChanges(elems, -1);

    cout << min(res1, res2) << endl;

    return 0;
}