import sys

class Journals:
	def solve(self):
		count = 0
		pos = 0
		check = False
		
		if len(self.input) == 2:
			print(0)
			return
		for i in range(2,len(self.input)-1,2):
			if self.input[i] == self.input[i-1]:
				pos += 1
				if pos == 2:
					pos = 0
					count +=1
			if pos == 1 and len(self.input)-2 == i:
				count += 1
		print(count)
		return
			
			
	def __init__(self):
		self.input = sys.stdin.read()
		self.input = self.input.strip()
		self.solve()
	

j = Journals()