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#include <iostream>
using namespace std;

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

    int n;
    cin >> n;
    int a[n], b[n];
    int result1 = 0, result2 = 0;
    for (int i=0; i<n; i++)
    {
        cin >> a[i];
        b[i] = a[i];
        if (i <= 0) continue;
        if (a[i-1] <= a[i] && i%2 == 0)
        {
            a[i] = -1000*1000*1000;
            result1++;
        }
        if (a[i-1] >= a[i] && i%2 == 1)
        {
            a[i] = 1000*1000*1000;
            result1++;
        }
        
        if (b[i-1] <= b[i] && i%2 == 1)
        {
            b[i] = -1000*1000*1000;
            result2++;
        }
        if (b[i-1] >= b[i] && i%2 == 0)
        {
            b[i] = 1000*1000*1000;
            result2++;
        }
    }
    cout << min(result1,result2) << endl;
}