#include <stdio.h>
int mid(int a,int b,int c){
    int max=a,min=a;
    if(b>max) max=b;
    if(c>max) max=c;
    
    if(b<min) min=b;
    if(c<min) min=c;
    
    return a+b+c-max-min;
}
int main(void){
    int a,b,c,md,k=0;
    scanf("%d%d%d",&c,&a,&b);
    while(~scanf("%d",&c)){
        md=mid(a,b,c);
        if(md-b&&a-b&&b-c&&a-c) k++;
        a=b;
        b=c;
    }
    printf("%d\n",k);
    return 0;
}