ch="ABCDEFGHIJKLMNOPQRSTUVWXYZ"
Set = set()
for i in range(26):
    for j in range(26):
        Set.add(ch[i]+ch[j])

def ad(x):
    Set.remove(x)
    ans.append(x)
ans=[]
for i in range(25):
    ad(ch[i]+ch[i])
    for j in range(i+2,26):
        ad(ch[i]+ch[j])
        ad(ch[j]+ch[i])
    ad(ch[i]+ch[i+1])
ad(ch[-1]+ch[-1])
for i in range(24,-1,-1):
    ad(ch[i+1]+ch[i])
for a in ans:
    print(a)