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#include <bits/stdc++.h>

using namespace std;

constexpr int MAXN = 5e4 + 20;

int n, a[MAXN];

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

    cin >> n;

    for (int i = 1; i <= n; i++)
        cin >> a[i];

    int res = 1e9 + 10;

    for (int k = 1; k <= 2; k++)
    {
        a[0] = -1e9; a[n+1] = -1e9;
        int tmp = 0;

        for (int i = k; i <= n; i+=2)
        {
            if (a[i] > a[i+1] && a[i] > a[i-1])
                continue;

            tmp++;    
        }
        res = min(tmp, res);

        a[0] = 1e9; a[n+1] = 1e9;
        tmp = 0;

        for (int i = k; i <= n; i+=2)
        {
            if (a[i] < a[i+1] && a[i] < a[i-1])
                continue;
            
            tmp++;
        }
        res = min(tmp, res);
    }

    cout << res;
}