import sys

MOD = 998244353

def main():
    S = sys.stdin.readline().strip()
    
    # 'A' pozitsiyalarini topish
    positions = []
    for i, ch in enumerate(S):
        if ch == 'A':
            positions.append(i)
    
    n = len(positions)
    if n == 0:
        print(1)
        return
    
    # Har bir 'A' uchun B qiymatini hisoblash
    B = [0] * n
    for i in range(n):
        # pozitsiya - oldingi 'A' lar soni
        B[i] = positions[i] + 1 - i
    
    # DP: dp[x] = oxirgi qiymati x bo'lgan ketma-ketliklar soni
    max_val = max(B)
    dp = [0] * (max_val + 2)
    
    # Birinchi 'A' uchun
    start = 0  # A[0] = 0
    end = B[0]
    for x in range(start, end):
        dp[x] = 1
    
    # Prefix sum massivi
    prefix = [0] * (max_val + 2)
    
    # Keyingi 'A' lar uchun
    for i in range(1, n):
        # Prefix sumni yangilash
        prefix[0] = 0
        for x in range(max_val + 1):
            prefix[x + 1] = (prefix[x] + dp[x]) % MOD
        
        # Yangi DP qiymatlarini hisoblash
        new_dp = [0] * (max_val + 2)
        start = 0  # A[i] = 0 (masala shartiga ko'ra)
        end = B[i]
        
        for x in range(start, end):
            new_dp[x] = prefix[x + 1]  # barcha <= x qiymatlari yig'indisi
        
        dp = new_dp
    
    # Natija
    result = sum(dp) % MOD
    print(result)

if __name__ == "__main__":
    main()