Fix string case.py

# In this Kata, you will be given a string that may have mixed uppercase and lowercase letters and your task is to convert that string to either lowercase only or uppercase only based on:

#     make as few changes as possible.
#     if the string contains equal number of uppercase and lowercase letters, convert the string to lowercase.

# For example:

# solve("coDe") = "code". Lowercase characters > uppercase. Change only the "D" to lowercase.
# solve("CODe") = "CODE". Uppercase characters > lowecase. Change only the "e" to uppercase.
# solve("coDE") = "code". Upper == lowercase. Change all to lowercase.

# More examples in test cases. Good luck!

def solve(s):
    lower = 'abcdefghijklmnopqrstuvwxyz'
    upper = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
    count = 0
    for i in s:
        if i in lower: 
            count -= 1
        else:
            count += 1
    return s.upper() if count > 0 else s.lower()