import sys

MOD = 998244353

def main():
    S = sys.stdin.readline().strip()
    
    # 'A' lar uchun B qiymatlarini hisoblash
    B = []
    cnt = 0
    for i, ch in enumerate(S):
        if ch == 'A':
            # i+1 - cnt = pozitsiya - oldingi 'A' lar soni
            B.append(i + 1 - cnt)
            cnt += 1
    
    N = len(B)
    if N == 0:
        print(1)
        return
    
    # A massivini yaratish (eng kichik qiymatlar)
    A = [0] * N
    for i in range(1, N):
        A[i] = max(A[i], A[i - 1])
    
    # DP[j] = oxirgi elementi j bo'lgan ketma-ketliklar soni
    max_val = B[-1]
    dp = [0] * (max_val + 2)
    
    # Birinchi 'A' uchun boshlang'ich holat
    for j in range(A[0], B[0]):
        dp[j] = 1
    
    # Har bir keyingi 'A' uchun
    for i in range(1, N):
        new_dp = [0] * (max_val + 2)
        
        # Prefix sum hisoblash
        prefix = [0] * (max_val + 2)
        for j in range(max_val + 1):
            prefix[j + 1] = (prefix[j] + dp[j]) % MOD
        
        # Yangi qiymatlarni hisoblash
        for j in range(A[i], B[i]):
            # Barcha oldingi qiymatlar <= j uchun
            new_dp[j] = prefix[j + 1] % MOD
        
        dp = new_dp
    
    # Natijani hisoblash
    result = sum(dp) % MOD
    print(result)

if __name__ == "__main__":
    main()