def alternatingCharacters(s):
    # Write your code here
    
    char_map = {}
    last_letter_seen = None
    
    if len(s) <= 1:
        return 0
    
    for each_char in s:
        if each_char not in char_map:
            char_map[each_char] = [1]
        else:
            if last_letter_seen is not None:
                if last_letter_seen == each_char:
                    char_map[each_char][-1]+=1
                else:
                    char_map[each_char].append(1)
        
        last_letter_seen = each_char
        
    min_deletions = 0
    
    for char, occ in char_map.items():
        min_deletions += sum(occ) - len(occ)
    
    return min_deletions