_n = gets
str = gets

def count(str)
  return 2 if str.length == 1
  
  str2 = str.chars.reject { |c| str[0] == c }.join('')
  if str2.length > 0
    count(str[1..-1]) + count(str2)
  else
    count(str[1..-1]) + 1
  end
end

puts count(str.strip) - 1