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#include <iostream>
#include <unordered_set>
#include <queue>
#include <cassert>
#include <algorithm>
#include <vector>
#include <set>
#include <map>
#include <numeric>
#include <assert.h>
#include <tuple>

using namespace std;
using ull = unsigned long long;
using ll = long long;


#ifdef GGDEBUG
#define dbg printf
#else 
#define dbg //dbg
#endif

#define MAX (1000000000)
// #define MAX (20)

int tab1[51000];
int tab2[51000];




int main() {
    int n;
    cin >> n;

    for (int i = 0; i < n; ++i) {
        scanf("%d", &tab1[i]);
        tab2[i] = tab1[i];
    }

    int changes = 0;
    // 1st try - FIRST is UP
    bool increasing = true;
    for (int i = 0; i < n-1; ++i) {
        if (increasing) {
            if (tab1[i+1] > tab1[i]) {
                // OK, no need to change
            } else {
                // change tab[i+1] so it is increasing
                tab1[i + 1] = MAX;
                changes++;
            }
        } else {
            if (tab1[i+1] < tab1[i]) {
                // OK, no need to change
            } else {
                // change tab[i+1] so it is decreasing
                tab1[i + 1] = -MAX;
                changes++;
            }
        }
        increasing = !increasing;
    }

    int changes2 = 0;
    // 2nd try - FIRST is DOWN
    increasing = false;
    for (int i = 0; i < n-1; ++i) {
        if (increasing) {
            if (tab2[i+1] > tab2[i]) {
                // OK, no need to change
            } else {
                // change tab[i+1] so it is increasing
                tab2[i + 1] = MAX;
                dbg("change2 tab[%d]\n", i + 1);
                changes2++;
            }
        } else {
            if (tab2[i+1] < tab2[i]) {
                // OK, no need to change
            } else {
                // change tab[i+1] so it is decreasing
                dbg("change2 tab[%d]\n", i + 1);
                tab2[i + 1] = -MAX;
                changes2++;
            }
        }
        increasing = !increasing;
    }

    dbg("%d %d\n", changes, changes2);

    // for (int i = 0; i < n; ++i)
    // {
    //     dbg("%d ", tab2[i]);
    // }
    // dbg("\n");
    cout << std::min(changes, changes2) << endl;
    // dupa;
    return 0;
}