#ifndef HIDDEN_IN_VS // 折りたたみ用 // 警告の抑制 #define _CRT_SECURE_NO_WARNINGS // ライブラリの読み込み #include using namespace std; // 型名の短縮 using ll = long long; // -2^63 ~ 2^63 = 9 * 10^18(int は -2^31 ~ 2^31 = 2 * 10^9) using pii = pair; using pll = pair; using pil = pair; using pli = pair; using vi = vector; using vvi = vector; using vvvi = vector; using vl = vector; using vvl = vector; using vvvl = vector; using vb = vector; using vvb = vector; using vvvb = vector; using vc = vector; using vvc = vector; using vvvc = vector; using vd = vector; using vvd = vector; using vvvd = vector; template using priority_queue_rev = priority_queue, greater>; using Graph = vvi; // 定数の定義 const double PI = acos(-1); const vi DX = { 1, 0, -1, 0 }; // 4 近傍(下,右,上,左) const vi DY = { 0, 1, 0, -1 }; int INF = 1001001001; ll INFL = 4004004004004004004LL; double EPS = 1e-12; // 入出力高速化 struct fast_io { fast_io() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(18); } } fastIOtmp; // 汎用マクロの定義 #define all(a) (a).begin(), (a).end() #define sz(x) ((int)(x).size()) #define lbpos(a, x) (int)distance((a).begin(), std::lower_bound(all(a), x)) #define ubpos(a, x) (int)distance((a).begin(), std::upper_bound(all(a), x)) #define Yes(b) {cout << ((b) ? "Yes\n" : "No\n");} #define rep(i, n) for(int i = 0, i##_len = int(n); i < i##_len; ++i) // 0 から n-1 まで昇順 #define repi(i, s, t) for(int i = int(s), i##_end = int(t); i <= i##_end; ++i) // s から t まで昇順 #define repir(i, s, t) for(int i = int(s), i##_end = int(t); i >= i##_end; --i) // s から t まで降順 #define repe(v, a) for(const auto& v : (a)) // a の全要素(変更不可能) #define repea(v, a) for(auto& v : (a)) // a の全要素(変更可能) #define repb(set, d) for(int set = 0; set < (1 << int(d)); ++set) // d ビット全探索(昇順) #define repp(a) sort(all(a)); for(bool a##_perm = true; a##_perm; a##_perm = next_permutation(all(a))) // a の順列全て(昇順) #define smod(n, m) ((((n) % (m)) + (m)) % (m)) // 非負mod #define uniq(a) {sort(all(a)); (a).erase(unique(all(a)), (a).end());} // 重複除去 #define EXIT(a) {cout << (a) << endl; exit(0);} // 強制終了 // 汎用関数の定義 template inline ll pow(T n, int k) { ll v = 1; rep(i, k) v *= n; return v; } template inline bool chmax(T& M, const T& x) { if (M < x) { M = x; return true; } return false; } // 最大値を更新(更新されたら true を返す) template inline bool chmin(T& m, const T& x) { if (m > x) { m = x; return true; } return false; } // 最小値を更新(更新されたら true を返す) // 演算子オーバーロード template inline istream& operator>>(istream& is, pair& p) { is >> p.first >> p.second; return is; } template inline istream& operator>>(istream& is, vector& v) { repea(x, v) is >> x; return is; } template inline vector& operator--(vector& v) { repea(x, v) --x; return v; } template inline vector& operator++(vector& v) { repea(x, v) ++x; return v; } // 手元環境(Visual Studio) #ifdef _MSC_VER #include "local.hpp" // 提出用(gcc) #else inline int popcount(int n) { return __builtin_popcount(n); } inline int popcount(ll n) { return __builtin_popcountll(n); } inline int lsb(int n) { return n != 0 ? __builtin_ctz(n) : -1; } inline int lsb(ll n) { return n != 0 ? __builtin_ctzll(n) : -1; } inline int msb(int n) { return n != 0 ? (31 - __builtin_clz(n)) : -1; } inline int msb(ll n) { return n != 0 ? (63 - __builtin_clzll(n)) : -1; } #define gcd __gcd #define dump(...) #define dumpel(v) #define dump_list(v) #define dump_list2D(v) #define input_from_file(f) #define output_to_file(f) #define Assert(b) { if (!(b)) while (1) cout << "OLE"; } #endif #endif // 折りたたみ用 #if __has_include() #include using namespace atcoder; //using mint = modint1000000007; using mint = modint998244353; //using mint = modint; // mint::set_mod(m); istream& operator>>(istream& is, mint& x) { ll x_; is >> x_; x = x_; return is; } ostream& operator<<(ostream& os, const mint& x) { os << x.val(); return os; } using vm = vector; using vvm = vector; using vvvm = vector; #endif template T naive(int n, int m) { vector>> dp(n + 1, vector>(n + 1, vector(m + 1))); vector>> acc(n + 1, vector>(n + 1, vector(m + 1))); dp[0][0][0] = 1; repi(i1, 1, n) repi(i2, 1, n) repi(j, 0, m) { acc[i1][i2][j] = acc[i1 - 1][i2][j] + acc[i1][i2 - 1][j] - acc[i1 - 1][i2 - 1][j] + dp[i1 - 1][i2 - 1][j]; int nj = j - abs(i1 - i2); if (nj >= 0) dp[i1][i2][j] += acc[i1][i2][nj]; } T res = 0; repi(i1, 0, n) repi(i2, 0, n) res += dp[i1][i2][m]; return res; } void zikken() { int N = 20; vvl a(N, vl(N)); rep(n, N) rep(m, N) a[m][n] = naive(n, m); dump_list2D(a); exit(0); } /* {{1,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768,65536,131072,262144,524288}, {0,0,2,8,24,64,160,384,896,2048,4608,10240,22528,49152,106496,229376,491520,1048576,2228224,4718592}, {0,0,0,4,20,72,224,640,1728,4480,11264,27648,66560,157696,368640,851968,1949696,4423680,9961472,22282240}, {0,0,0,0,8,48,200,704,2240,6656,18816,51200,135168,348160,878592,2179072,5324800,12845056,30638080,72351744}, {0,0,0,0,2,24,136,592,2224,7584,24128,72832,210944,590848,1609728,4284416,11177984,28663808,72400896,180453376}, {0,0,0,0,0,8,72,400,1792,7040,25248,84608,268928,819200,2409472,6881280,19165184,52232192,139681792,367362048}, {0,0,0,0,0,4,40,256,1304,5760,22976,84800,294336,971904,3079168,9420800,27975680,80957440,229048320,635256832}, {0,0,0,0,0,0,18,152,888,4352,19040,76544,287744,1023744,3478144,11362304,35885056,110051328,328904704,960790528}, {0,0,0,0,0,0,8,92,604,3208,15072,64896,260832,990208,3581312,12422400,41548032,134584832,423781376,1301170176}, {0,0,0,0,0,0,2,48,392,2304,11600,52992,225280,903552,3449472,12616448,44435456,151343104,500244992,1609582592}, {0,0,0,0,0,0,0,24,250,1640,8824,42464,189248,794624,3175040,12153088,44784000,159506432,550928384,1850614784}, {0,0,0,0,0,0,0,8,144,1120,6568,33440,155904,681856,2833760,11278720,43219840,160083968,574948352,2007638016}, {0,0,0,0,0,0,0,4,84,764,4864,26128,126992,576064,2477952,10201408,40435008,154953088,575923200,2081435648}, {0,0,0,0,0,0,0,0,40,488,3514,20152,102360,481024,2135552,9060352,36993280,146042880,559348736,2083796992}, {0,0,0,0,0,0,0,0,18,304,2504,15428,81988,398664,1822496,7945088,33306016,134978560,530804608,2031044608}, {0,0,0,0,0,0,0,0,8,176,1726,11624,65088,328080,1543512,6902080,29635776,122956544,495003648,1939467264}, {0,0,0,0,0,0,0,0,2,100,1168,8672,51370,268728,1300456,5956656,26147344,110813472,455597760,1823197312}, {0,0,0,0,0,0,0,0,0,48,750,6312,40072,218680,1090184,5113712,22922304,99071360,415180480,1693380864}, {0,0,0,0,0,0,0,0,0,24,472,4528,30980,177020,910360,4372896,20000520,88046464,375518528,1558339968}, {0,0,0,0,0,0,0,0,0,8,278,3144,23560,142064,756370,3725016,17383032,77885888,337691584,1423864064}} */ mint solve(int n, int m) { int K = (int)(sqrt(m) + 1); // dp_i[j][k] : 長さ i,総和 j, 高さ k のパスのスコア和 vvm dp(m + 1, vm(K + 1)); dp[0][0] = 1; rep(i, n) { vvm ndp(m + 1, vm(K + 1)); repi(j, 0, m) repi(k, 0, K) { // 上がる if (j + k + 1 <= m && k + 1 <= K) { ndp[j + k + 1][k + 1] += dp[j][k] * (k == 0 ? 2 : 1); } // 水平 if (j + k <= m) ndp[j + k][k] += dp[j][k] * 2; // 下がる if (j + k - 1 <= m && k - 1 >= 0) { ndp[j + k - 1][k - 1] += dp[j][k]; } } dp = move(ndp); dump("------", i, "------"); dumpel(dp); } return dp[m][0]; } int main() { // input_from_file("input.txt"); // output_to_file("output.txt"); // zikken(); int n, m; cin >> n >> m; dump(naive(n, m)); cout << solve(n, m) << endl; }