program W
implicit none
integer::N
integer,allocatable,dimension(:)::A
integer::ANS=0
integer::i
read*,N
allocate(A(N))
read*,A
do i=1,N-2
    if(A(i)/=A(i+2).and.(A(i+1)-A(i))*(A(i+1)-A(i+2))>0)ANS=ANS+1
end do
print"(I0)",ANS
end program W