def next_check(cubes):
	index_list = []
	for cube_index in range(1, len(cubes)):
		if cube_index not in index_list and cubes[cube_index] == cubes[cube_index - 1]:
			index_list.append(cube_index - 1)
			index_list.append(cube_index)
	l = len(index_list)
	for i in reversed(index_list):
		cubes.pop(i)
	return (cubes, l)


cubes = input()
for c in cubes:
	if c not in ['0', '1']:
		exit(0)
cube_list = []
for cube in cubes:
	cube_list.append(cube)
l = len(cube_list)
k = 0
while (l != 0):
	cubes, l = next_check(cube_list)
	k += l
print(k)