with open('5.txt') as file:
    string = file.readline()

data = []
for letter in string:
    data.append(letter)

indx = 1000 #uprzedzający pytania - wartość z dupy :D
while indx > 1:
    for i in range(len(data)-1, 0 , -1):
        if abs(ord(data[i-1]) - ord(data[i])) == 32:
            ix = i
            data.pop(i)
            data.pop(i-1)
            break
        indx = i
print(len(data))