chars = gets.chomp.chars
sort_chars = chars.sort
i = 0
j = 1
fault = false
while j <= sort_chars.length
  unless sort_chars[i] == sort_chars[j]
    fault = true
    break
  end
  i += 2
  j += 2
end

half = chars.length / 2
k,l = 0,half
while k < half
  unless chars[k] == chars[l]
    fault = true
    break
  end
  k += 1
  l += 1
end

puts fault ? "NO" : "YES"