def fun_exercise_6(x):
    for i in range(len(x)):
        if 97 <= ord(x[i]) <= 108 or 65 <= ord(x[i]) <= 76:
            x = x[:i] + x[i].lower() + x[i+1:]
        else:
            x = x[:i] + x[i].upper() + x[i+1:]
    return x

def fun_exercise_8(x):
    letter_amt = []
    for letter in x:
        if letter not in letter_amt:
            letter_amt.extend([letter, 1])
        else:
            letter_amt[letter_amt.index(letter) + 1] += 1
    return letter_amt[letter_amt.index(sorted([num for num in letter_amt if isinstance(num, int)], reverse=True)[1])-1]