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#include <bits/stdc++.h>

using namespace std;

int a1[50500];
int a2[50500];

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

    int n;
    cin >> n;

    for(int i = 0; i < n; i++) {
        cin >> a1[i];
        a2[i] = a1[i];
    }

    int c1 = 0;
    int c2 = 0;
    for(int i = 1; i < n; i++) {
        if(i%2) {
            if(a1[i] > a1[i -1]) {
            } else {
                a1[i] = 2000000;
                c1++;
            }

            if(a2[i] < a2[i -1]) {
            } else {
                a2[i] = -2000000;
                c2++;
            }
        } else {
            if(a1[i] < a1[i -1]) {
            } else {
                a1[i] = -2000000;
                c1++;
            }

            if(a2[i] > a2[i -1]) {
            } else {
                a2[i] = 2000000;
                c2++;
            }
        }
    }

    cout << min(c1, c2) << endl;

    return 0;
}