C. The Fair Nut and Stringtime limit per test1 secondmemory limit per test256 megabytesinputstandard inputoutputstandard outputThe Fair Nut found a string s. The string consists of lowercase Latin letters. The Nut is a curious guy, so he wants to find the number of strictly increasing sequences p_1, p_2, \ldots, p_k, such that:   For each i (1 \leq i \leq k), s_{p_i} = 'a'.  For each i (1 \leq i < k), there is such j that p_i < j < p_{i + 1} and s_j = 'b'. The Nut is upset because he doesn't know how to find the number. Help him.This number should be calculated modulo 10^9 + 7.InputThe first line contains the string s (1 \leq |s| \leq 10^5) consisting of lowercase Latin letters.OutputIn a single line print the answer to the problem — the number of such sequences p_1, p_2, \ldots, p_k modulo 10^9 + 7.ExamplesInputabbaaOutput5InputbaaaaOutput4InputagaaOutput3NoteIn the first example, there are 5 possible sequences. [1], [4], [5], [1, 4], [1, 5].In the second example, there are 4 possible sequences. [2], [3], [4], [5].In the third example, there are 3 possible sequences. [1], [3], [4].
Inputabbaa
Output5
['combinatorics', 'dp', 'implementation', '*1500']