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#include <iostream>
#include <cstdio>

using namespace std;

int main()
{
    int tmp;
    bool last_forward = true;
    bool last_backward = true;
    int zmiany_forward = 0;
    int zmiany_backward = 0;
    int n;
    string in = "";
    scanf("%i", &n);
    int tab_forward[n];
    int tab_backward[n];
    for(int i = 0; i<n;i++){
        scanf("%i", &tmp);
        tab_forward[i] = tmp;
        tab_backward[n-i-1] = tmp;
    }
    for(int i = 1; i<n-1;i++){
        if(tab_forward[i-1] > tab_forward[i] && tab_forward[i] < tab_forward[i+1]){
            last_forward = true;
        }
        else if(tab_forward[i-1] < tab_forward[i] && tab_forward[i] > tab_forward[i+1]){
            last_forward = false;
        }
        else if(tab_forward[i-1] > tab_forward[i] && tab_forward[i] > tab_forward[i+1]){
            tab_forward[i+1] = 1000001;
            zmiany_forward++;
            last_forward = true;
        }
        else if(tab_forward[i-1] < tab_forward[i] && tab_forward[i] < tab_forward[i+1]){
            tab_forward[i+1] = -1000001;
            zmiany_forward++;
            last_forward = false;
        }
        else if(tab_forward[i-1] > tab_forward[i] && tab_forward[i] == tab_forward[i+1]){
            tab_forward[i+1] = 1000001;
            zmiany_forward++;
            last_forward = true;
        }
        else if(tab_forward[i-1] < tab_forward[i] && tab_forward[i] == tab_forward[i+1]){
            tab_forward[i+1] = -1000001;
            zmiany_forward++;
            last_forward = false;
        }
        else if(tab_forward[i-1] == tab_forward[i] && tab_forward[i] == tab_forward[i+1]){
            if(last_forward){
                tab_forward[i] = -1000001;
            }
            else{
                tab_forward[i] = 1000001;
            }
            zmiany_forward++;
        }

        if(tab_backward[i-1] > tab_backward[i] && tab_backward[i] < tab_backward[i+1]){
            last_backward = true;
        }
        else if(tab_backward[i-1] < tab_backward[i] && tab_backward[i] > tab_backward[i+1]){
            last_backward = false;
        }
        else if(tab_backward[i-1] > tab_backward[i] && tab_backward[i] > tab_backward[i+1]){
            tab_backward[i+1] = 1000001;
            zmiany_backward++;
            last_backward = true;
        }
        else if(tab_backward[i-1] < tab_backward[i] && tab_backward[i] < tab_backward[i+1]){
            tab_backward[i+1] = -1000001;
            zmiany_backward++;
            last_backward = false;
        }
        else if(tab_backward[i-1] > tab_backward[i] && tab_backward[i] == tab_backward[i+1]){
            tab_backward[i+1] = 1000001;
            zmiany_backward++;
            last_backward = true;
        }
        else if(tab_backward[i-1] < tab_backward[i] && tab_backward[i] == tab_backward[i+1]){
            tab_backward[i+1] = -1000001;
            zmiany_backward++;
            last_backward = false;
        }
        else if(tab_backward[i-1] == tab_backward[i] && tab_backward[i] == tab_backward[i+1]){
            if(last_backward){
                tab_backward[i] = -1000001;
            }
            else{
                tab_backward[i] = 1000001;
            }
            zmiany_backward++;
        }
    }
    if(zmiany_backward < zmiany_forward) {
        zmiany_forward = zmiany_backward;
    }
    printf("%i", zmiany_forward);
    return 0;
}