Minimum number of stepsjava

We have a string of letters 'a' and 'b'. We want to perform some operations on it. On each step we choose one of substrings "ab" in the string and replace it with the string "bba". If we have no "ab" as a substring, our job is done. Print the minimum number of steps we should perform to make our job done modulo109 + 7.

The string "ab" appears as a substring if there is a letter 'b' right after the letter 'a' somewhere in the string.

Input

The first line contains the initial string consisting of letters 'a' and 'b' only with length from1 to106.

Output

Print the minimum number of steps modulo 109 + 7.

Examples

Input

ab

Output

1

Input

aab

Output

3

Note

The first example: "ab"  →  "bba".

The second example: "aab"  →  "abba"  →  "bbaba" →  "bbbbaa".

题意：把ab变成ba的样式，每一次翻转a都能把b变成二倍，最后不再出现ab的情况 记录翻转次数..

import java.util.Scanner; public class Main { public static void main(String[] args) { Scanner sc = new Scanner(System.in); while (sc.hasNext()) { String a = sc.next(); long q = 0; long sum = 0; for (int i = a.length() - 1; i >= 0; i--) { if (a.charAt(i) == 'b') { q++; } else { sum += q; q = q * 2; } sum = sum % 1000000007; q = q % 1000000007; } System.out.println(sum % 1000000007); } } }