#include #define fi first #define se second #define rep(i,s,n) for (int i = (s); i < (n); ++i) #define rrep(i,n,g) for (int i = (n)-1; i >= (g); --i) #define all(a) a.begin(),a.end() #define rall(a) a.rbegin(),a.rend() #define len(x) (int)(x).size() #define dup(x,y) (((x)+(y)-1)/(y)) #define pb push_back #define eb emplace_back #define Field(T) vector> using namespace std; using ll = long long; using ull = unsigned long long; template using pq = priority_queue,greater>; using P = pair; templatebool chmax(T&a,T b){if(abool chmin(T&a,T b){if(b struct ModInt { int x; ModInt() : x(0) {} ModInt(int64_t y) : x(y >= 0 ? y % mod : (mod - (-y) % mod) % mod) {} ModInt &operator+=(const ModInt &p) { if((x += p.x) >= mod) x -= mod; return *this; } ModInt &operator-=(const ModInt &p) { if((x += mod - p.x) >= mod) x -= mod; return *this; } ModInt &operator*=(const ModInt &p) { x = (int) (1LL * x * p.x % mod); return *this; } ModInt &operator/=(const ModInt &p) { *this *= p.inverse(); return *this; } ModInt operator-() const { return ModInt(-x); } ModInt operator+(const ModInt &p) const { return ModInt(*this) += p; } ModInt operator-(const ModInt &p) const { return ModInt(*this) -= p; } ModInt operator*(const ModInt &p) const { return ModInt(*this) *= p; } ModInt operator/(const ModInt &p) const { return ModInt(*this) /= p; } bool operator==(const ModInt &p) const { return x == p.x; } bool operator!=(const ModInt &p) const { return x != p.x; } ModInt inverse() const { assert(x); int a = x, b = mod, u = 1, v = 0, t; while(b > 0) { t = a / b; swap(a -= t * b, b); swap(u -= t * v, v); } return ModInt(u); } ModInt pow(int64_t n) const { ModInt ret(1), mul(x); while(n > 0) { if(n & 1) ret *= mul; mul *= mul; n >>= 1; } return ret; } friend ostream &operator<<(ostream &os, const ModInt &p) { return os << p.x; } friend istream &operator>>(istream &is, ModInt &a) { int64_t t; is >> t; a = ModInt< mod >(t); return (is); } static int get_mod() { return mod; } }; using mint = ModInt<998244353>; int main() { function f = [](int n, int k) { vector dp(k+1), ndp(k+1); dp[0] = 1; rep(i,0,2*n) { fill(all(ndp), 0); rep(j,0,k+1) { if (j < k) ndp[j+1] += dp[j]; if (j > 0) ndp[j-1] += dp[j]; } swap(dp, ndp); } return dp[0]; }; int n, k; cin >> n >> k; cout << f(n, k) - f(n, k-1) << endl; return 0; }