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#include <stdio.h>
#include <string.h>


int _max = 1000001;
int arr[50000], arr2[50000];
int main() {
    int n, r = 0;
    scanf("%d", &n);
    int last = 0;
    for(int i=0;i<n;i++) scanf(" %d", arr + i);

    
    memcpy(arr2, arr, sizeof(arr));
    int a1 = 0, a2 = 0;

    for(int i=1;i<n;i++) {
        int tmp = (i&1);
        if((tmp && arr2[i] >= arr2[i-1]) || (!tmp && arr2[i] <= arr2[i-1])) {
            arr2[i] = (tmp ? -1 : 1) * _max;
            a1++;
        } 
    }

   /* for(int i=0;i<n;i++)
        printf("%d ", arr2[i]);
    putchar(10);*/

    for(int i=1;i<n;i++) {
        int tmp = !(i&1);
        if((tmp && arr[i] >= arr[i-1]) || (!tmp && arr[i] <= arr[i-1])) {
            arr[i] = (tmp ? -1 : 1) * _max;
            a2++;
        } 
    }
    //printf("%d %d\n", a1, a2);
    printf("%d\n", a1 < a2 ? a1 : a2);
    
    return 0;
}