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 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))
 		    	  	 	   			 		    					