main(n,i,s){scanf("%d",&n);int *a;a=malloc(sizeof(int)*n);for(i=0;i<n;i++)scanf("%d",&a[i]);s=0;for(i=0;i<n-2;i++)(a[i]<a[i+1]&&a[i+1]>a[i+2]||a[i]>a[i+1]&&a[i+1]<a[i+2])&&a[i]!=a[i+2]?s++:0;printf("%d",s);}