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 = raw_input()

res = 1
cnt = 1

for c in s:
    if c == 'a':
        cnt += 1
    elif c == 'b':
        res = MD(res*cnt)
        cnt = 1

res = MD(res*cnt)

print MD(res-1)
		 	  		 		  	 		       		 		