aaaaabb
 aabaaaa
 babbabaabbbbabwbvbhbbbaaabbabbbbbbbkabbbbabaaabbbbbbajabbaaabazbbbzbalbabbwbbaabbabacabdbabbbfaaabbb
 baaahbbbba
 ababavvvv
 abnxabbaab
 krflnzhter
 amaabbbbxaabbbabaabaabbaaabaaaaabibbabaabaaabaabcaaxabablbbbbmbbbaaaaaabbaabbbaaabaaaababaababbabbbb
 babbbaaaaaabbbaabaaaaaoaabababaababaaaaababaaaaaaabbbbbbaaapaabaaabaaababaaaabaaaabaaaaababaaaabaaab

5
 14
 42467327
 7
 7
 11
 0
 98718509
 813881762

mod = 1000000007

def MD(x):
	return ((x%mod) + mod) % mod
	
s = input()
res = 1
cnt = 1
for e in s:
	if e == "a":
		cnt += 1
	elif e == "b":
		res = MD(res*cnt)
		cnt = 1
res = MD(res*cnt)
	
print(MD(res-1))

 		 	 	  		      	  		 	    			