import sys

MOD = 998244353

def main():
    data = sys.stdin.read().strip()
    if not data:
        return
    
    # A harflarini hisoblash
    B = []
    cnt = 0
    for i, ch in enumerate(data, 1):
        if ch == 'A':
            B.append(i - cnt)
            cnt += 1
    
    if not B:
        print(1)
        return
    
    m = len(B)
    
    # DP jadvali
    max_val = B[-1]
    dp = [0] * (max_val)
    
    # Boshlang'ich to'ldirish
    for j in range(B[0]):
        dp[j] = 1
    
    # Har bir keyingi A uchun
    for i in range(1, m):
        end = B[i]
        
        # Prefix sumni hisoblash va yangi dp ni bir vaqtda
        new_dp = [0] * max_val
        current_sum = 0
        
        for j in range(end):
            current_sum = (current_sum + dp[j]) % MOD
            new_dp[j] = current_sum
        
        dp = new_dp
    
    # Natija
    result = 0
    for j in range(max_val):
        result = (result + dp[j]) % MOD
    
    print(result)

if __name__ == "__main__":
    main()