d='ABCDEFGHIJKLMNOPQRSTUVWXYZ@'
q=['A']
ans=['AA']
n=26
for l in range(1,n):
  for r in range(l*2):
    if r%2==0:
      ans+=q[r]+d[l],
    else:
      if r<len(q):
        ans+=d[l]+q[r],
      else:
        ans+=d[l]+'A',
  q+=[d[l]]*2
p=1
for i in range(len(ans)):
  print(ans[i])
  if ans[i][1]==d[p]:
    print(d[p]*2)
    p+=1