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

int check1(vector<int> v)
{
    int ans = 0;
    int n = v.size();
    for(int i = 1; i < n; i++)
    {
        if(i % 2 && v[i] <= v[i-1])
        {
            v[i] = 1e9;
            ans++;
        }
        else if(i % 2 == 0 && v[i] >= v[i -1])
        {
            v[i] = -1e9;
            ans++;
        }
    }
    return ans;
}

int check2(vector<int> v)
{
    int ans = 0;
    int n = v.size();
    for(int i = 1; i < n; i++)
    {
        if(i % 2 == 0 && v[i] <= v[i-1])
        {
            v[i] = 1e9;
            ans++;
        }
        else if(i % 2 && v[i] >= v[i -1])
        {
            v[i] = -1e9;
            ans++;
        }
    }
    return ans;
}

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

    int n;
    cin >> n;
    vector<int> v(n);

    for(int i = 0; i < n; i++)
        cin >> v[i];

    int ans = min(check1(v), check2(v));
    cout << ans << '\n';
}