aaaaabb
 aabaaaa
 babbabaabbbbabwbvbhbbbaaabbabbbbbbbkabbbbabaaabbbbbbajabbaaabazbbbzbalbabbwbbaabbabacabdbabbbfaaabbb
 baaahbbbba
 ababavvvv
 abnxabbaab
 krflnzhter
 amaabbbbxaabbbabaabaabbaaabaaaaabibbabaabaaabaabcaaxabablbbbbmbbbaaaaaabbaabbbaaabaaaababaababbabbbb
 babbbaaaaaabbbaabaaaaaoaabababaababaaaaababaaaaaaabbbbbbaaapaabaaabaaababaaaabaaaabaaaaababaaaabaaab

5
 14
 42467327
 7
 7
 11
 0
 98718509
 813881762

inp = list(input())
lis = []
new_inp = []

for i in range(len(inp)):
    if inp[i]=='a' or inp[i]=='b':
        new_inp.append(inp[i])

i=0
mul = []
while i<len(new_inp):
    if new_inp[i]=='a':
        j=i
        while j<len(new_inp) and new_inp[j]=='a':
            j+=1
        mul.append(j-i)
        i=j+1
    else:
        i+=1

ans = 1
for k in mul:
    ans = ans*(k+1)

print(ans-1)








# arr,brr = [0]*len(inp),[0]*len(inp)
# ans=0
# for i in range(len(inp)):
#     if inp[i] == 'a':
#         arr[i]=1
#         ans+=1
#     elif inp[i] == 'b':
#         brr[i] = 1

# i=0
# while i<len(arr)-1:
#     if arr[i] == 1:
#         j=i+1
#         while j<len(brr) and brr[j]!=1:
#             j+=1
#         if j<len(brr) and brr[j]==1:
#             ans += sum(arr[:i+1]) * sum(arr[j:])
#         i=j
#     else:
#         i+=1

# ans = ans%1000000007
# print(ans)