integer::N,i,kadomatsu=0
  integer,allocatable::a(:)
  read *, N
  allocate(a(N))
  read *, a
  do i=1,N-2
     if(a(i).ne.a(i+2)) then
        if((a(i).lt.a(i+1).and.a(i+2).lt.a(i+1)).or. &
             (a(i).gt.a(i+1).and.a(i+2).gt.a(i+1))) then
           kadomatsu = kadomatsu + 1
        end if
     end if
  end do
  print '(i0)',kadomatsu
end program