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

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

    int n, a[50000], changes = 0;
    int even = 0, odd = 0; // amnt of: even - a[2n] > a[2n-1]; odd - a[2n+1] > a[2n]; n1 = 1
    bool asc = 1;
    cin >> n;
    for (int i=0; i<n; i++)
        cin >> a[i];
    
    for (int i=0; i<n-1; i++) {
        if (a[i+1] != a[i]) {
            if ((a[i+1] > a[i] && i%2 == 0) || (a[i+1] < a[i] && i%2 == 1))
                even++;
            else
                odd++;
        }
    }
    if (odd > even)
        asc = 0;

    int i=0;
    while (i+1<n) {
        if (asc && a[i+1] <= a[i]) {
            changes++; i++;
        }
        else if (!asc && a[i+1] >= a[i]) {
            changes++; i++;
        }
        else {
            if (asc)    asc = 0;
            else        asc = 1;
        }
        i++;
    }

    cout << changes;
}