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#include <iostream>

int n;
long long rising[50007];
long long dropping[50007];
long long alt;

const long long stuff = 1 << 20;

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

    std::cin >> n;

    for (int i = 0; i < n; i++) {
        std::cin >> alt;
        rising[i] = alt;
        dropping[i] = alt;
    }

    // Rising
    int rising_min = 0;
    for (int i = 1; i < n; i++) {
        if (i & 1) {
            if (rising[i] <= rising[i-1]) {
                rising_min++;
                rising[i] = stuff;
            }
        } else {
            if (rising[i] >= rising[i-1]) {
                rising_min++;
                rising[i] = -stuff;
            }
        }
    }

    // Dropping
    int dropping_min = 0;
    for (int i = 1; i < n; i++) {
        if (i & 1) {
            if (dropping[i] >= dropping[i-1]) {
                dropping_min++;
                dropping[i] = -stuff;
            }
        } else {
            if (dropping[i] <= dropping[i-1]) {
                dropping_min++;
                dropping[i] = stuff;
            }
        }
    }

    if (rising_min < dropping_min) {
        std::cout << rising_min;
    } else {
        std::cout << dropping_min;
    }
}