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 shanky_ty
 */
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);
        TaskC solver = new TaskC();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskC {
        public void solve(int testNumber, Scanner in, PrintWriter out) {
            String n = in.nextLine();
            int mod = 1000000007;
            int res = 1;
            int cnt = 0;
            for (int i = 0; i < n.length(); i++) {
                if (n.charAt(i) == 'a') {
                    cnt++;
                } else if (n.charAt(i) == 'b') {
                    res = res * (cnt + 1);
                    cnt = 0;
                }
            }
            if (cnt > 0) {
                res = ((res % mod) * ((cnt + 1) % mod)) % mod;
            }
            out.write(Integer.toString((res % mod - 1 % mod) % mod));
        }

    }
}

