alpha_small_ = [chr(i) for i in range(97, 97+26)] #アルファベッドの小文字

n = int(input())
ans = []
def solve(now,i):
    if len(now) == n:
        ans.append(now)
        return
    for j in range(i+1):
        solve(now+alpha_small_[j],max(i,j+1))

solve("a",1)


for x in sorted(ans):
    print(x)

print(len(ans))