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#include<cstdio>
#include<algorithm>
using namespace std;

#define N_MAX 50005

int n;
int input[N_MAX];
int resa,resb;

int main()
{
  scanf("%d", &n);
  for(int i=0;i<n;i++) {
    scanf("%d", input+i);
  }
  resa=0;
  resb=0;
  bool pop=false;
  //wariant NW
  //printf("Wariant NW\n");
  for(int i=1;i<n;i++) {
    if(i%2==0) {
      //N
      if(pop == true) {
        pop = false;
      } else {
        if(input[i]>=input[i-1]) {
          //printf("FLIP N: %d\n",i);
          resa++;
          pop = true;
        }
      }
    } else {
      //W
      if(pop == true) {
        pop = false;
      } else {
        if(input[i]<=input[i-1]) {
          //printf("FLIP W: %d\n",i);
          resa++;
          pop = true;
        }
      }
    }
  }
  //wariant WN
  pop=false;
  //printf("Wariant WN\n");
  for(int i=1;i<n;i++) {
    if(i%2==1) {
      //N
      if(pop == true) {
        pop = false;
      } else {
        if(input[i]>=input[i-1]) {
          //printf("FLIP N: %d\n",i);
          resb++;
          pop = true;
        }
      }
    } else {
      //W
      if(pop == true) {
        pop = false;
      } else {
        if(input[i]<=input[i-1]) {
          //printf("FLIP W: %d\n",i);
          resb++;
          pop = true;
        }
      }
    }
  }
  if(resb < resa) resa=resb;
  printf("%d\n", resa);
  return 0;
}