aaaaabb
 aabaaaa
 babbabaabbbbabwbvbhbbbaaabbabbbbbbbkabbbbabaaabbbbbbajabbaaabazbbbzbalbabbwbbaabbabacabdbabbbfaaabbb
 baaahbbbba
 ababavvvv
 abnxabbaab
 krflnzhter
 amaabbbbxaabbbabaabaabbaaabaaaaabibbabaabaaabaabcaaxabablbbbbmbbbaaaaaabbaabbbaaabaaaababaababbabbbb
 babbbaaaaaabbbaabaaaaaoaabababaababaaaaababaaaaaaabbbbbbaaapaabaaabaaababaaaabaaaabaaaaababaaaabaaab

5
 14
 42467327
 7
 7
 11
 0
 98718509
 813881762

m = 10**(9)+7
s = input()
n = len(s)
a = 0
b = 0
table = [0]*(n+1)
dp = [0]*(n+1)
for i in range(n):
    if s[i] == 'a':
        a = a+1
        table[b] = table[b] +1
        c = b
    elif s[i] == 'b':
        b = b+1
dp[c] = table[c]
prev = c
su = table[c]
for i in range(c-1,-1,-1):
    if table[i] != 0:
        dp[i] = ((table[i]%m)*(dp[prev]%m))%m
        su = (su%m+table[i]%m)%m
        prev = i
print((dp[prev]%m+su%m)%m)
