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#include <stdio.h>
int main()
{
    int a,n=0,i,j;
    while(1){
        scanf("%d",&a);
        if(a==0) break;
        else{
            int ar[a];
            for(i=0; i<a; i++){
                scanf("%d",&ar[i]);
            }
            for(j=1; j<a-2; j++){
               if(ar[j]>ar[j+1] &&  ar[j]>ar[j-1])
               n+=1;
             else if(ar[j]<ar[j+1] &&  ar[j]<ar[j-1])
             n+=1;
            }

            if(ar[a-1]>ar[0] &&  ar[a-1]>ar[a-2]) n+=1;
             if(ar[a-1]<ar[0] &&  ar[a-1]<ar[a-2])
                n+=1;
                if(ar[0]>ar[1] &&  ar[0]>ar[a-1])
                n+=1;
                 if(ar[0]<ar[1] &&  ar[0]<ar[a-1])
                n+=1;
            }
            printf("%d\n",n);
            n=0;
            }

   return 0;
}