def inp() a=gets.chomp.split(" ").map(&:to_i)end 
def inpf() a=gets.chomp.split(" ").map(&:to_f)end
def inps() a=gets.chomp.split(" ")end  
def copy(a) Marshal.load(Marshal.dump(a)) end
def kaizyo(n)(n < 2)? 1 : (2..n).inject(:*) end
def scount(a) b=na(a.max+1);a.each{|n|b[n]+=1};return b end
def na(n,d=0) Array.new(n,d)end
def na2(n,m,d=0) Array.new(n){Array.new(m,d)}end
def na3(n,m,l,d=0) Array.new(n){Array.new(m){Array.new(l,d)}}end
def bit(n) a.to_s(2).split("").map(&:to_i) end
n =inp[0]
a =inp
c =0
(n-2).times do |x|
  c+= 1 if(a[x..x+2].uniq.size == 3 and(a[x+0] == a[x..x+2].sort[1] or a[x+2] == a[x..x+2].sort[1]) )
end
p c