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#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
int MAX =  1000001;
int MIN = -1000001;

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

    int n;
    cin >> n;

    vector<int> v1(n), v2(n);
    for (int i = 0; i < n; i++) {
        cin >> v1[i];
        v2[i] = v1[i];
    }

    int ra = 0;
    for (int i = 1; i < n; i++){
        if (i % 2 == 1) {
            if (v1[i] <= v1[i - 1]) {
                v1[i] = MAX;
                ra++;
            }
        }
        else {
            if (v1[i] >= v1[i - 1]) {
                v1[i] = MIN;
                ra++;
            }
        }
    }

    int rb = 0;
    for (int i = 1; i < n; i++){
        if (i % 2 == 0) {
            if (v2[i] <= v2[i - 1]) {
                v2[i] = MAX;
                rb++;
            }
        }
        else {
            if (v2[i] >= v2[i - 1]) {
                v2[i] = MIN;
                rb++;
            }
        }
    }

    cout << min(ra, rb);

    return 0;
}