def calcular_jogadas(entrada):
MOD = 1000000007
contagem_b = 0
jogadas = 0
indice = len(entrada) - 1
while indice >= 0:
letra = entrada[indice]
if letra != 'b':
jogadas = (jogadas + contagem_b) % MOD
contagem_b = (2 * contagem_b) % MOD
else:
contagem_b = (contagem_b + 1) % MOD
indice -= 1
return jogadas
entrada = input()
resultado = calcular_jogadas(entrada)
print(resultado)#include <bits/stdc++.h>
using namespace std;
const int N = 1e6 + 5;
const int M = 1e9 + 7;
int n;
long long ans, cnt;
char a[N];
int main() {
scanf("%s", a + 1);
n = strlen(a + 1);
for (int i = n; i >= 1; i--) {
if (a[i] == 'a') {
ans = (ans + cnt) % M;
cnt = cnt * 2 % M;
}
else if (a[i] == 'b'){
cnt++;
}
// cout << cnt << ' ' << ans << ' ' << i << endl;
}
printf("%lld", ans);
return 0;
}
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