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#include <iostream>
#include <string>
#include <algorithm>


using namespace std;

int sgn(int a) {
    return (0 < a) - (a < 0);
}


int main() {

    std::ios_base::sync_with_stdio(false);
    std::cin.tie(NULL);


    int sequence[50000];
    int temp[50000];
    int count;
    int result1 = 100000;
    int result2 = 100000;
    int result3 = 100000;

    cin >> count;


    for (int i = 0; i < count; i++) {
        cin >> sequence[i];
    }
    int prev = 0;
    int prevPrev = 0;

    result1 = 0;
    for (int i = 0; i < count; i++) {

        if (i == 1) {
            prevPrev = sgn(sequence[i] - sequence[i - 1]);
            prev = sgn(sequence[i + 1] - sequence[i]);
            if (prevPrev != 1 || prev != -1) {
                result1++;
                prevPrev = 1;
                prev = -1;
            }
        }

        if (i > 1) {
            if (i > 2) {
                prevPrev = prev;
                prev = sgn(sequence[i] - temp[i - 1]);
            }
            if (prevPrev == 1 && prev != -1) {
                result1++;
                prev = -1;
                temp[i] = -2000000;
            } else if (prevPrev == -1 && prev != 1) {
                result1++;
                prev = 1;
                temp[i] = 2000000;
            } else {
                temp[i] = sequence[i];
            }
        }
//        cout << "up:  i: " << i << ", prevPrev: " << prevPrev << ", prev: " << prev << ", result: " << result1 << "\n";

    }
    result2 = 0;
    for (int i = 0; i < count; i++) {

        if (i == 1) {
            prevPrev = sgn(sequence[i] - sequence[i - 1]);
            prev = sgn(sequence[i + 1] - sequence[i]);
            if (prevPrev != -1 || prev != 1) {
                result2++;
                prevPrev = -1;
                prev = 1;
            }
        }

        if (i > 1) {
            if (i > 2) {
                prevPrev = prev;
                prev = sgn(sequence[i] - temp[i - 1]);
            }
            if (prevPrev == 1 && prev != -1) {
                result2++;
                prev = -1;
                temp[i] = -2000000;
            } else if (prevPrev == -1 && prev != 1) {
                result2++;
                prev = 1;
                temp[i] = 2000000;
            } else {
                temp[i] = sequence[i];
            }
        }
//        cout << "down:  i: " << i << ", prevPrev: " << prevPrev << ", prev: " << prev << ", result: " << result2
//             << "\n";

    }

    if (sequence[0] != sequence[1]) {
        result3 = 0;
        for (int i = 0; i < count; i++) {
            if (i == 1) {
                prevPrev = sgn(sequence[i] - sequence[i - 1]);
                prev = sgn(sequence[i + 1] - sequence[i]);
            }

            if (i > 1) {
                if (i > 2) {
                    prevPrev = prev;
                    prev = sgn(sequence[i] - temp[i - 1]);
                }
                if (prevPrev == 1 && prev != -1) {
                    result3++;
                    prev = -1;
                    temp[i] = -2000000;
                } else if (prevPrev == -1 && prev != 1) {
                    result3++;
                    prev = 1;
                    temp[i] = 2000000;
                } else {
                    temp[i] = sequence[i];
                }
            }
//            cout << "nothing:  i: " << i << ", prevPrev: " << prevPrev << ", prev: " << prev << ", result: " << result3
//                 << "\n";

        }
    }

        cout <<  min(result1, min(result2, result3)) << "\n";

    return 0;
}