input: def count_uppercase_vowels_even_indices(s):
      """
      Given a string s, count the number of uppercase vowels located on even positions.
      
      For example:
      count_uppercase_vowels_even_indices('aBCdEf') returns 1
      count_uppercase_vowels_even_indices('abcdefg') returns 0
      count_uppercase_vowels_even_indices('dBBE') returns 0
      """
output:     count = 0
      uppercase_vowels = {'A', 'E', 'I', 'O', 'U'}
      for i in range(0, len(s), 2):
          if s[i] in uppercase_vowels:
              count += 1
      return count