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#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <queue>
#include <map>
#include <set>
#include <stack>
#include <cmath>
using namespace std;

int n_number, numbers[50001], is_correct[50001];

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    cin >> n_number;
    for (int i = 1; i <= n_number; i++)
        cin >> numbers[i];
    int best = 1e9, current = 0;
    bool last = 1;
    is_correct[0] = 2;
    for (int i = 1; i <= n_number; i++) {
        is_correct[i] = last;
        last = 0;
        if ((i % 2 && numbers[i] > numbers[i + 1]) || (i % 2 == 0 && numbers[i] < numbers[i + 1])) {
            last = 1;
            is_correct[i]++;
        }
        if (is_correct[i] == 0 || (is_correct[i] == 1 && is_correct[i - 1] == 1)) {
            current++; 
            last = 1;
            is_correct[i] = 2;
        }
    }
    best = current;
    current = 0;
    last = 1;
    for (int i = 1; i <= n_number; i++) {
        is_correct[i] = last;
        last = 0;
        if ((i % 2 && numbers[i] < numbers[i + 1]) || (i % 2 == 0 && numbers[i] > numbers[i + 1])) {
            last = 1;
            is_correct[i]++;
        }
        if (is_correct[i] == 0 || (is_correct[i] == 1 && is_correct[i - 1] == 1)) {
            current++;
            last = 1;
            is_correct[i] = 2;
        }
    }
    cout << min(best, current);
}