#include <bits/stdc++.h>
using namespace std;
#define int              long long int
#define double           long double
#define print(a)         for(auto x : a) cout << x << " "; cout << endl


const int M = 1000000007;
const int N = 3e5+9;
const int INF = 2e9+1;
const int LINF = 2000000000000000001;

inline int power(int a, int b, int mod=M) {
    int x = 1;
    a %= mod;
    while (b) {
        if (b & 1) x = (x * a) % mod; 
        a = (a * a) % mod;
        b >>= 1;
    }
    return x;
}



//_ ***************************** START Below *******************************


string a;

int consistency(int n){

    string b;
    for(int i=0; i<n; i++){
        if(a[i] == 'a' || a[i] == 'b') b.push_back(a[i]); 
    }

    n = b.size();

    int ans = 1;
    int i=0;

    while(i<n){
        while(i<n && b[i] == 'b') i++;
        if(i==n) break;

        int j = i+1;
        while(j<n && b[j] == 'a') j++;
        int ct = j-i;
        ans = (ans * (ct+1))%M;
        i = j;
    }

    return ans-1 ;
}















int practice(int n){


    return 0;
}





void solve() {
    
    cin >> a;
    int n = a.size();    

    cout << consistency(n) << endl;


}





int32_t main() {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

    int t = 1;
    while (t--) {
        solve();
    }

    return 0;
}