import sys
line=[int(c) for c in sys.stdin.rstrip()]
length=len(line)
while True:
  line2=[]
  for i in range(len(line)-1):
    if line[i]!=2 and line[i]!=line[i+1]:
      line[i]=2
      line[i+1]=2
    elif line[i]!=2:
      line2.append(line[i])
  if len(line)!=0 and line[len(line)-1]!=2:
      line2.append(line[len(line)-1])
  if 2 in line:
    line=[i for i in line2]
  else:
    break
print(length-len(line))