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#include <bits/stdc++.h>

using namespace std;

constexpr int MAXN = 5e4 + 7;
int a[MAXN], b[MAXN];

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

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

    int rosnie_maleje = 0;
    for(int i = 2; i <= n; i++) {
        if(i % 2 == 0) {
            if(a[i] - a[i-1] <= 0) {
                rosnie_maleje++;
                a[i] = 1e6 + 1;
            }
        }
        else {
            if(a[i] - a[i-1] >= 0) {
                rosnie_maleje++;
                a[i] = -(1e6 + 1);
            }
        }
    }

    int maleje_rosnie = 0;
    for(int i = 2; i <= n; i++) {
        if(i % 2 == 0) {
            if(b[i] - b[i-1] >= 0) {
                maleje_rosnie++;
                b[i] = -(1e6 + 1);
            }
        }
        else {
            if(b[i] - b[i-1] <= 0) {
                maleje_rosnie++;
                b[i] = 1e6 + 1;
            }
        }
    }

    cout << min(rosnie_maleje, maleje_rosnie);

    return 0;
}