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#include <cstdio>

int main() {
    int n;
    scanf("%d", &n);
    int* rec = new int[n + 1];

    for (int i = 0; i < n; ++i) {
        scanf("%i", &rec[i]);
    }

    int min = 0;
    int max = 0;
    int last_idx_min = 0;
    int last_idx_max = 0;

    for (int i = 1; i < n - 1; ++i) {
        if (rec[i - 1] < rec[i] && rec[i] > rec[i + 1]) {
            if (i % 2 == 0) {
                if (((i - last_idx_max) % 3 == 0 || last_idx_max == 0) && ((i - last_idx_max) <= 2 || last_idx_max == 0 || (i - last_idx_max) % 2 == 0)) {
                    max+=3;
                    last_idx_max = i;
                }
                else if ((i-last_idx_max)%3 != 0) {
                    max+=(i-last_idx_max)%3;
                    last_idx_max = i;
                }else {
                    last_idx_max = 0;
                }
            } else {
                if (((i - last_idx_min) % 3 == 0 || last_idx_min == 0) && ((i - last_idx_min) <= 2 || last_idx_min == 0 || (i - last_idx_min) % 2 == 0)) {
                    min+=3;
                    last_idx_min = i;
                }
                else if ((i-last_idx_min)%3 != 0) {
                    min+=(i-last_idx_min)%3;
                }else {
                    last_idx_min = 0;
                }
            }
        } else if (rec[i - 1] > rec[i] && rec[i] < rec[i + 1]) {
            if (i % 2 == 0) {
                if (((i - last_idx_min) % 3 == 0 || last_idx_min == 0) && ((i - last_idx_min) <= 2 || last_idx_min == 0 || (i - last_idx_min) % 2 == 0)) {
                    min+=3;
                    last_idx_min = i;
                }
                else if ((i-last_idx_min)%3 != 0) {
                    min+=(i-last_idx_min)%3;
                    last_idx_min = i;
                } else {
                    last_idx_min = 0;
                }
            } else {
                if (((i - last_idx_max) % 3 == 0 || last_idx_max == 0) && ((i - last_idx_max) <= 2 || last_idx_max == 0 || (i - last_idx_max) % 2 == 0)) {
                    max+=3;
                    last_idx_max = i;
                    last_idx_min = 0;
                }
                else if ((i-last_idx_max)%3 != 0)  {
                    max+=(i-last_idx_max)%3;
                    last_idx_max = i;
                }else {
                    last_idx_max = 0;
                }
            }
        }
    }

    if (max > min) {
        printf("%d", ((n - max) / 2) + (n - max) % 2);
    } else {
        printf("%d", ((n - min) / 2));
    }

    return 0;
}