# The key to solving this problem is to realize the shortest iterable string component of an unordered alphabetic string is made up by all the unique letters.

seq = input()

def min_itr_len(sequence):
    uni_list = []
    for char in sequence:
        if char not in uni_list:
            uni_list.append(char)
    return len(uni_list)

print(min_itr_len(seq))