#!/usr/bin/env python3
from string import ascii_lowercase, ascii_uppercase
import fileinput
import re


def main():
    removals = set(map(''.join, zip(ascii_lowercase, ascii_uppercase)))
    removals = removals.union({r[::-1] for r in removals})
    remove_regex = re.compile('({})'.format('|'.join(removals)))
    line = next(fileinput.input()).strip()
    count = 1
    while count > 0:
        line, count = remove_regex.subn('', line)
    return len(line)


if __name__ == '__main__':
    print(main())