from string import ascii_lowercase

n,k=map(int,raw_input().split());
st = []
for i in range(n):
	s = raw_input();
	st.append(s);

for c in ascii_lowercase:
	cnt = 0
	for ss in st:
		if c in ss:
			cnt += 1
	if cnt == n:
		k -= 1
print ":-)" if k <= 0 else ":-("