Recently, Anton has found a set. The set consists of small English letters. Anton carefully wrote out all the letters from the set in one line, separated by a comma. He also added an opening curved bracket at the beginning of the line and a closing curved bracket at the end of the line. 

Unfortunately, from time to time Anton would forget writing some letter and write it again. He asks you to count the total number of distinct letters in his set.
The first and the single line contains the set of letters. The length of the line doesn't exceed 1000. It is guaranteed that the line starts from an opening curved bracket and ends with a closing curved bracket. Between them, small English letters are listed, separated by a comma. Each comma is followed by a space.
def count_unique_letters(input_str):
    # 将输入的字符串转换为只包含小写字母的列表
    unique_letters = [char for char in input_str if char.islower()]
    
    # 统计列表中元素的个数
    result = len(unique_letters)
    
    return result

input_str = input("请输入一行字符，长度在1000以内，仅包括小写字母、'{'、'}' 和空格：")
count = count_unique_letters(input_str)
print(f"这一行中出现的不同字母个数为：{count}")
		          	  	 		   			 			