aaaaabb
 aabaaaa
 babbabaabbbbabwbvbhbbbaaabbabbbbbbbkabbbbabaaabbbbbbajabbaaabazbbbzbalbabbwbbaabbabacabdbabbbfaaabbb
 baaahbbbba
 ababavvvv
 abnxabbaab
 krflnzhter
 amaabbbbxaabbbabaabaabbaaabaaaaabibbabaabaaabaabcaaxabablbbbbmbbbaaaaaabbaabbbaaabaaaababaababbabbbb
 babbbaaaaaabbbaabaaaaaoaabababaababaaaaababaaaaaaabbbbbbaaapaabaaabaaababaaaabaaaabaaaaababaaaabaaab

5
 14
 42467327
 7
 7
 11
 0
 98718509
 813881762

// Working program with FastReader 
import java.io.BufferedReader; 
import java.io.IOException; 
import java.io.InputStreamReader; 
import java.util.Scanner; 
import java.util.StringTokenizer; 

public class Main 
{  
    public static void main(String[] args) 
	{ 
		FastReader sc=new FastReader(); 
    	String str=sc.next();
    	StringBuilder s = new StringBuilder();
    	for(int i=0;i<str.length();i++)
    	if(str.charAt(i) == 'a' || str.charAt(i) == 'b')
    	s=s.append(str.charAt(i));
    // 	System.out.println(s);
    	long res=0l;
    	long count=0l;
    	int i=0;
    	int len=s.length();
    	for( i=0;i<len;i++){
    	    if(s.charAt(i) == 'b' && count !=0) {
    	        res=res==0 ? count+1:(res*(count+1))%1000000007;
    	        count=0;
    	    }
    	    else if(s.charAt(i) == 'a')
    	    {
    	        count++;
    	    }
    	}
    	if(len>0 && s.charAt(i-1) == 'a')
    	res=res==0 ? count+1:(res*(count+1))%1000000007;
    	System.out.println(res==0?0:(res-1)%1000000007);
        	
    	
	} 
	
	static class FastReader 
	{ 
		BufferedReader br; 
		StringTokenizer st; 

		public FastReader() 
		{ 
			br = new BufferedReader(new
					InputStreamReader(System.in)); 
		} 

		String next() 
		{ 
			while (st == null || !st.hasMoreElements()) 
			{ 
				try
				{ 
					st = new StringTokenizer(br.readLine()); 
				} 
				catch (IOException e) 
				{ 
					e.printStackTrace(); 
				} 
			} 
			return st.nextToken(); 
		} 

		int nextInt() 
		{ 
			return Integer.parseInt(next()); 
		} 

		long nextLong() 
		{ 
			return Long.parseLong(next()); 
		} 

		double nextDouble() 
		{ 
			return Double.parseDouble(next()); 
		} 

		String nextLine() 
		{ 
			String str = ""; 
			try
			{ 
				str = br.readLine(); 
			} 
			catch (IOException e) 
			{ 
				e.printStackTrace(); 
			} 
			return str; 
		} 
	} 


} 
