#!/usr/bin/env python

def read_input():
    with open('input.txt', 'r') as f:
        data = f.read().splitlines()
        return data[0]

def find_longest_match(polymer):
    result = 1
    for x in range(len(polymer)-1):
        if abs(ord(polymer[x]) - ord(polymer[x+1])) != 32:
            break
        result += 1
    return result
            

polymer = read_input()
parsing_pos = 0

while parsing_pos < len(polymer):
    lm = find_longest_match(polymer[parsing_pos:])
    if lm < 2:
        parsing_pos += 1
        continue

#    print("found({}, {}) : {}".format(parsing_pos, lm,  polymer[parsing_pos:parsing_pos+lm]))

    lm = 2
    if parsing_pos == 0:
        polymer = polymer[lm:]
    else:
        polymer = polymer[:parsing_pos] + polymer[lm+parsing_pos:]
        parsing_pos -= 1

#    print("new polymer: {}".format(polymer))

print(len(polymer))