import string

txt = string.ascii_lowercase
S = input().strip() + ' '
S = S[0:len(S) // 2 * 2]

for i in range(len(S) // 2):
  if not(S[i*2] in txt):
    print('No')
    break
  
  if not(S[i*2+1] == ' '):
    print('No')
    break
else:
  print('Yes')