#include using namespace std; #include #include template class modint{ private: using T = long long; T a; public: constexpr modint(const long long x = 0) noexcept : a((x%mod+mod)%mod) {} constexpr T& value() noexcept { return a; } constexpr const T& value() const noexcept { return a; } constexpr modint operator-() const noexcept { return modint(0) -= *this; } constexpr modint operator+(const modint& rhs) const noexcept { return modint(*this) += rhs; } constexpr modint operator-(const modint& rhs) const noexcept { return modint(*this) -= rhs; } constexpr modint operator*(const modint& rhs) const noexcept { return modint(*this) *= rhs; } constexpr modint operator/(const modint& rhs) const noexcept { return modint(*this) /= rhs; } constexpr modint& operator+=(const modint& rhs) noexcept { a += rhs.a; if(a >= mod) a -= mod; return *this; } constexpr modint& operator-=(const modint& rhs) noexcept { if(a < rhs.a) a += mod; a -= rhs.a; return *this; } constexpr modint& operator*=(const modint& rhs) noexcept { a = a*rhs.a%mod; return *this; } constexpr modint& operator/=(const modint& rhs) noexcept { return *this *= rhs.inv(); } constexpr bool operator==(const modint& rhs) const noexcept { return a == rhs.a; } constexpr bool operator!=(const modint& rhs) const noexcept { return not (*this == rhs); } constexpr modint pow(long long k) const noexcept { modint ret(1); modint x = k > 0 ? *this : this->inv(); k = abs(k); while(k > 0){ if(k&1) ret *= x; x *= x; k >>= 1; } return ret; } constexpr modint inv() const noexcept { return pow(mod-2); } friend std::ostream& operator<<(std::ostream &os, const modint &X) noexcept { return os << X.a; } friend std::istream& operator>>(std::istream &is, modint &X) noexcept { is >> X.a; X.a %= mod; if(X.a < 0) X.a += mod; return is; } }; #include #include template struct Combination { private: int sz; vector F, F_; public: Combination(int sz) : sz(sz), F(sz+1), F_(sz+1) { F[0] = 1; for(int i = 0; i < sz; ++i) F[i+1] = F[i]*(i+1); F_.back() = (T)1/F.back(); for(int i = sz-1; i >= 0; --i) F_[i] = F_[i+1]*(i+1); } T C(int n, int k){ assert(n <= sz); if(n < 0 or k > n) return (T)0; return F[n]*F_[k]*F_[n-k]; } T P(int n, int k){ assert(n <= sz); if(n < 0 or k > n) return (T)0; return F[n]*F_[n-k]; } }; int main(){ using mint = modint<998244353>; int n, k; cin >> n >> k; if(n == 1){ int ans[] = {1,1,3,6,3,1,1}; cout << ans[k] << '\n'; return 0; } Combination comb(n*2+4); mint ans = comb.C(n*2+4,k); if(k%2 == 0){ if(n%2){ cerr << "a" << '\n'; ans += comb.C(n+3,k/2)*3; }else{ cerr << "b" << '\n'; ans += comb.C(n+2,k/2)*3; } }else if(n%2){ cerr << "c" << '\n'; ans += comb.C(n+1,k/2)*2; } cout << ans/4 << '\n'; }