import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

import numpy as np

"""
・累積和の到達地点集合ごとに見る
・type1：X未満で終わる
・type2：X+1以上2X未満
・type3：2X以上、これはXが奇数の場合のみ
"""

MOD = 998244353

N,X = map(int,read().split())

def cumprod(arr,MOD):
    L = len(arr); Lsq = int(L**.5+1)
    arr = np.resize(arr,Lsq**2).reshape(Lsq,Lsq)
    for n in range(1,Lsq):
        arr[:,n] *= arr[:,n-1]; arr[:,n] %= MOD
    for n in range(1,Lsq):
        arr[n] *= arr[n-1,-1]; arr[n] %= MOD
    return arr.ravel()[:L]

def make_fact(U,MOD):
    x = np.arange(U,dtype=np.int64); x[0] = 1
    fact = cumprod(x,MOD)
    x = np.arange(U,0,-1,dtype=np.int64); x[0] = pow(int(fact[-1]),MOD-2,MOD)
    fact_inv = cumprod(x,MOD)[::-1]
    return fact,fact_inv

U = N+100
fact,fact_inv = make_fact(U,MOD)
combN = fact[N] * fact_inv[:N+1] % MOD * fact_inv[N::-1] % MOD

def F1(N,X):
    # X未満で終わる場合
    def mult(P,Q):
        # 多項式の積
        dP = len(P) - 1
        dQ = len(Q) - 1
        if dP < dQ:
            dP,dQ = dQ,dP
            P,Q = Q,P
        R = np.zeros(dP+dQ+1,np.int64)
        for n in range(dQ+1):
            R[n:n+dP+1] += Q[n] * P % MOD
        R %= MOD
        return R[:X]
    def power(P,n):
        if n == 0:
            return np.array([1],dtype=np.int64)
        Q = power(P,n//2)
        Q = mult(Q,Q)
        return mult(P,Q) if n&1 else Q
    P = np.array([1,1,1],np.int64)
    Q = power(P,N)
    return Q.sum() % MOD

def F2(N,X):
    U = N+100
    fact,fact_inv = make_fact(U,MOD)
    combN = fact[N] * fact_inv[:N+1] % MOD * fact_inv[N::-1] % MOD
    x = np.zeros(N+1,np.int64)
    # X+1+2nで終わる場合
    for n in range(X):
        m = (X-1) - (2+2*n)
        if m < 0:
            break
        # 2+2n -> X-1に含まれる2の回数ごとに
        two = np.arange(m//2+1,dtype=np.int64)
        one = m - 2*two
        coef = fact[one+two] * fact_inv[one] % MOD * fact_inv[two] % MOD
        rest = N-one-two-(2*n+2)
        ind = rest>=0
        rest = rest[ind]; coef = coef[ind]
        x[rest] += coef
    x %= MOD
    return (x * combN % MOD).sum() % MOD

def F3(N,X):
    U = N+100
    fact,fact_inv = make_fact(U,MOD)
    combN = fact[N] * fact_inv[:N+1] % MOD * fact_inv[N::-1] % MOD
    # 2X以上の偶数。Xは奇数で、+2を連打している場合
    if X%2 == 0:
        return 0
    if X > N:
        return 0
    n = N-X+1
    return combN[:n].sum() % MOD

answer = (F1(N,X) + F2(N,X) + F3(N,X)) % MOD
print(answer)

### FIXED CODE ###

import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

import numpy as np

"""
・累積和の到達地点集合ごとに見る
・type1：X未満で終わる
・type2：X+1以上2X未満
・type3：2X以上、これはXが奇数の場合のみ
"""

MOD = 998244353

N,X = map(int,read().split())

def cumprod(arr,MOD):
    L = len(arr); Lsq = int(L**.5+1)
    arr = np.resize(arr,Lsq**2).reshape(Lsq,Lsq)
    for n in range(1,Lsq):
        arr[:,n] *= arr[:,n-1]; arr[:,n] %= MOD
    for n in range(1,Lsq):
        arr[n] *= arr[n-1,-1]; arr[n] %= MOD
    return arr.ravel()[:L]

def make_fact(U,MOD):
    x = np.arange(U,dtype=np.int64); x[0] = 1
    fact = cumprod(x,MOD)
    x = np.arange(U,0,-1,dtype=np.int64); x[0] = pow(int(fact[-1]),MOD-2,MOD)
    fact_inv = cumprod(x,MOD)[::-1]
    return fact,fact_inv

U = N+N+100
fact,fact_inv = make_fact(U,MOD)
combN = fact[N] * fact_inv[:N+1] % MOD * fact_inv[N::-1] % MOD

def F1(N,X):
    # X未満で終わる場合
    def mult(P,Q):
        # 多項式の積
        dP = len(P) - 1
        dQ = len(Q) - 1
        if dP < dQ:
            dP,dQ = dQ,dP
            P,Q = Q,P
        R = np.zeros(dP+dQ+1,np.int64)
        for n in range(dQ+1):
            R[n:n+dP+1] += Q[n] * P % MOD
        R %= MOD
        return R[:X]
    def power(P,n):
        if n == 0:
            return np.array([1],dtype=np.int64)
        Q = power(P,n//2)
        Q = mult(Q,Q)
        return mult(P,Q) if n&1 else Q
    P = np.array([1,1,1],np.int64)
    Q = power(P,N)
    return Q.sum() % MOD

def F2(N,X):
    x = np.zeros(N+1,np.int64)
    # X+1+2nで終わる場合
    for n in range(X):
        m = (X-1) - (2+2*n)
        if m < 0:
            break
        # 2+2n -> X-1に含まれる2の回数ごとに
        two = np.arange(m//2+1,dtype=np.int64)
        one = m - 2*two
        coef = fact[one+two] * fact_inv[one] % MOD * fact_inv[two] % MOD
        rest = N-one-two-(2*n+2)
        ind = rest>=0
        rest = rest[ind]; coef = coef[ind]
        x[rest] += coef
    x %= MOD
    return (x * combN % MOD).sum() % MOD

def F3(N,X):
    # 2X以上の偶数。Xは奇数で、+2を連打している場合
    if X%2 == 0:
        return 0
    if X > N:
        return 0
    n = N-X+1
    return combN[:n].sum() % MOD

answer = (F1(N,X) + F2(N,X) + F3(N,X)) % MOD
print(answer)