aaaaabb
 aabaaaa
 babbabaabbbbabwbvbhbbbaaabbabbbbbbbkabbbbabaaabbbbbbajabbaaabazbbbzbalbabbwbbaabbabacabdbabbbfaaabbb
 baaahbbbba
 ababavvvv
 abnxabbaab
 krflnzhter
 amaabbbbxaabbbabaabaabbaaabaaaaabibbabaabaaabaabcaaxabablbbbbmbbbaaaaaabbaabbbaaabaaaababaababbabbbb
 babbbaaaaaabbbaabaaaaaoaabababaababaaaaababaaaaaaabbbbbbaaapaabaaabaaababaaaabaaaabaaaaababaaaabaaab

5
 14
 42467327
 7
 7
 11
 0
 98718509
 813881762

import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Scanner;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author DHV
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        Scanner in = new Scanner(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        CTheFairNutAndString solver = new CTheFairNutAndString();
        solver.solve(1, in, out);
        out.close();
    }

    static class CTheFairNutAndString {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            final int MOD = (int) (1e9 + 7);
            String s = in.next();
            int res = 0;
            int seq = 0;
            for (int i = 0; i < s.length(); i++) {
                if (s.charAt(i) == 'a') {
                    res += seq + 1;
                    res %= MOD;
                } else if (s.charAt(i) == 'b') {
                    seq = res;
                }
            }
            out.println(res);
        }

    }
}

