def next_check(cubes):
	index_list = []
	for cube_index in reversed(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)

def main():
	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)

if __name__ == "__main__":
	main()