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

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

    int n;
    cin >> n;
    int op1 = 0, op2 = 0;
    int cur, prev;
    bool skip1 = false, skip2 = false;
    for(int i = 0; i < n; i++)
    {
        cin >> cur;
        if(i > 0)
        {
            if(!skip1 && ((cur >= prev && i % 2) || (cur <= prev && !(i % 2))))
            {
                op1++;
                skip1 = true;
            }
            else skip1 = false;
            if(!skip2 && ((cur <= prev && i % 2) || (cur >= prev && !(i % 2))))
            {
                op2++;
                skip2 = true;
            }
            else skip2 = false;
        }
        prev = cur;
    }
    cout << min(op1, op2);
}