def sgets = gets.strip
def get_int = Integer(sgets)
def get_list = sgets.split
def get_int_list = get_list.map { Integer(_1) }
def puts_yn(b) = puts(b ? 'Yes' : 'No')

s = sgets
sz = s.size
if sz <= 2
  puts 0
else
  n = (0..sz-3).count do |i|
    t = s[i,3]
    m = t[1]
    (t[0] == m) ^ (m == t[2])
  end
  puts n
end