#pragma region satashun // #pragma GCC optimize("Ofast") // #pragma GCC optimize("unroll-loops") #include using namespace std; using uint = unsigned int; using ll = long long; using ull = unsigned long long; using pii = pair; template using V = vector; template using VV = V>; template V make_vec(size_t a) { return V(a); } template auto make_vec(size_t a, Ts... ts) { return V(ts...))>(a, make_vec(ts...)); } template void fill_vec(T& v, const V& val) { v = val; } template void fill_vec(vector& vec, const V& val) { for (auto& v : vec) fill_vec(v, val); } #define pb push_back #define eb emplace_back #define mp make_pair #define fi first #define se second #define rep(i, n) rep2(i, 0, n) #define rep2(i, m, n) for (int i = m; i < (n); i++) #define per(i, b) per2(i, 0, b) #define per2(i, a, b) for (int i = int(b) - 1; i >= int(a); i--) #define ALL(c) (c).begin(), (c).end() #define SZ(x) ((int)(x).size()) constexpr ll TEN(int n) { return (n == 0) ? 1 : 10 * TEN(n - 1); } template void chmin(T& t, const U& u) { if (t > u) t = u; } template void chmax(T& t, const U& u) { if (t < u) t = u; } template int arglb(const V& v, const T& x) { return distance(v.begin(), lower_bound(ALL(v), x)); } template int argub(const V& v, const T& x) { return distance(v.begin(), upper_bound(ALL(v), x)); } template void mkuni(vector& v) { sort(ALL(v)); v.erase(unique(ALL(v)), end(v)); } template vector sort_by(const vector& v, bool increasing = true) { vector res(v.size()); iota(res.begin(), res.end(), 0); if (increasing) { stable_sort(res.begin(), res.end(), [&](int i, int j) { return v[i] < v[j]; }); } else { stable_sort(res.begin(), res.end(), [&](int i, int j) { return v[i] > v[j]; }); } return res; } template istream& operator>>(istream& is, pair& p) { is >> p.first >> p.second; return is; } template ostream& operator<<(ostream& os, const pair& p) { os << "(" << p.first << "," << p.second << ")"; return os; } template istream& operator>>(istream& is, vector& v) { for (auto& x : v) { is >> x; } return is; } template ostream& operator<<(ostream& os, const vector& v) { os << "{"; rep(i, v.size()) { if (i) os << ","; os << v[i]; } os << "}"; return os; } template ostream& operator<<(ostream& os, const set& ST) { os << "{"; for (auto it = ST.begin(); it != ST.end(); ++it) { if (it != ST.begin()) os << ","; os << *it; } os << "}"; return os; } template ostream& operator<<(ostream& os, const multiset& ST) { os << "{"; for (auto it = ST.begin(); it != ST.end(); ++it) { if (it != ST.begin()) os << ","; os << *it; } os << "}"; return os; } template ostream& operator<<(ostream& os, const map& MP) { for (auto it = MP.begin(); it != MP.end(); ++it) { os << "(" << it->first << ": " << it->second << ")"; } return os; } string to_string(__int128_t x) { if (x == 0) return "0"; string result; if (x < 0) { result += "-"; x *= -1; } string t; while (x) { t.push_back('0' + x % 10); x /= 10; } reverse(t.begin(), t.end()); return result + t; } ostream& operator<<(ostream& o, __int128_t x) { return o << to_string(x); } #ifdef LOCAL void debug_out() { cerr << endl; } template void debug_out(Head H, Tail... T) { cerr << " " << H; debug_out(T...); } #define debug(...) \ cerr << __LINE__ << " [" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__) #define dump(x) cerr << __LINE__ << " " << #x << " = " << (x) << endl #else #define debug(...) (void(0)) #define dump(x) (void(0)) #endif template V& operator+=(V& vec, const T& v) { for (auto& x : vec) x += v; return vec; } template V& operator-=(V& vec, const T& v) { for (auto& x : vec) x -= v; return vec; } // suc : 1 = newline, 2 = space template void print(T x, int suc = 1) { cout << x; if (suc == 1) cout << "\n"; else if (suc == 2) cout << " "; } template void print(const vector& v, int suc = 1) { for (int i = 0; i < v.size(); ++i) print(v[i], i == int(v.size()) - 1 ? suc : 2); } template void show(T x) { print(x, 1); } template void show(Head H, Tail... T) { print(H, 2); show(T...); } int topbit(int t) { return t == 0 ? -1 : 31 - __builtin_clz(t); } int topbit(ll t) { return t == 0 ? -1 : 63 - __builtin_clzll(t); } int botbit(int a) { return a == 0 ? 32 : __builtin_ctz(a); } int botbit(ll a) { return a == 0 ? 64 : __builtin_ctzll(a); } int popcount(int t) { return __builtin_popcount(t); } int popcount(ll t) { return __builtin_popcountll(t); } int bit_parity(int t) { return __builtin_parity(t); } int bit_parity(ll t) { return __builtin_parityll(t); } struct prepare_io { prepare_io() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(10); } } prep_io; #pragma endregion satashun template struct ModInt { using uint = unsigned int; using ull = unsigned long long; using M = ModInt; uint v; ModInt(ll _v = 0) { set_norm(_v % MOD + MOD); } M& set_norm(uint _v) { //[0, MOD * 2)->[0, MOD) v = (_v < MOD) ? _v : _v - MOD; return *this; } explicit operator bool() const { return v != 0; } explicit operator int() const { return v; } M operator+(const M& a) const { return M().set_norm(v + a.v); } M operator-(const M& a) const { return M().set_norm(v + MOD - a.v); } M operator*(const M& a) const { return M().set_norm(ull(v) * a.v % MOD); } M operator/(const M& a) const { return *this * a.inv(); } M& operator+=(const M& a) { return *this = *this + a; } M& operator-=(const M& a) { return *this = *this - a; } M& operator*=(const M& a) { return *this = *this * a; } M& operator/=(const M& a) { return *this = *this / a; } M operator-() const { return M() - *this; } M& operator++(int) { return *this = *this + 1; } M& operator--(int) { return *this = *this - 1; } M pow(ll n) const { if (n < 0) return inv().pow(-n); M x = *this, res = 1; while (n) { if (n & 1) res *= x; x *= x; n >>= 1; } return res; } M inv() const { ll a = v, b = MOD, p = 1, q = 0, t; while (b != 0) { t = a / b; swap(a -= t * b, b); swap(p -= t * q, q); } return M(p); } friend ostream& operator<<(ostream& os, const M& a) { return os << a.v; } friend istream& operator>>(istream& in, M& x) { ll v_; in >> v_; x = M(v_); return in; } bool operator<(const M& r) const { return v < r.v; } bool operator>(const M& r) const { return v < *this; } bool operator<=(const M& r) const { return !(r < *this); } bool operator>=(const M& r) const { return !(*this < r); } bool operator==(const M& a) const { return v == a.v; } bool operator!=(const M& a) const { return v != a.v; } static uint get_mod() { return MOD; } }; // using Mint = ModInt<1000000007>; using Mint = ModInt<998244353>; V fact, ifact, inv; VV small_comb; void mod_init() { const int maxv = 1000010; const int maxvv = 5000; fact.resize(maxv); ifact.resize(maxv); inv.resize(maxv); small_comb = make_vec(maxvv, maxvv); fact[0] = 1; for (int i = 1; i < maxv; ++i) { fact[i] = fact[i - 1] * i; } ifact[maxv - 1] = fact[maxv - 1].inv(); for (int i = maxv - 2; i >= 0; --i) { ifact[i] = ifact[i + 1] * (i + 1); } for (int i = 1; i < maxv; ++i) { inv[i] = ifact[i] * fact[i - 1]; } for (int i = 0; i < maxvv; ++i) { small_comb[i][0] = small_comb[i][i] = 1; for (int j = 1; j < i; ++j) { small_comb[i][j] = small_comb[i - 1][j] + small_comb[i - 1][j - 1]; } } } Mint comb(int n, int r) { if (n < 0 || r < 0 || r > n) return Mint(0); if (n < small_comb.size()) return small_comb[n][r]; return fact[n] * ifact[r] * ifact[n - r]; } Mint inv_comb(int n, int r) { if (n < 0 || r < 0 || r > n) return Mint(0); return ifact[n] * fact[r] * fact[n - r]; } // O(k) Mint comb_slow(ll n, ll k) { if (n < 0 || k < 0 || k > n) return Mint(0); Mint res = ifact[k]; for (int i = 0; i < k; ++i) { res = res * (n - i); } return res; } // line up // a 'o' + b 'x' Mint comb2(int a, int b) { if (a < 0 || b < 0) return 0; return comb(a + b, a); } // divide a into b groups Mint nhr(int a, int b) { if (b == 0) return Mint(a == 0); return comb(a + b - 1, a); } // O(p + log_p n) Mint lucas(ll n, ll k, int p) { if (n < 0 || k < 0 || k > n) return Mint(0); Mint res = 1; while (n > 0) { res *= comb(n % p, k % p); n /= p; k /= p; } return res; } struct ModPrepare { ModPrepare() { mod_init(); } } prep_mod; /** * @docs docs/ntt.md */ template struct NumberTheoreticTransform { D root; V roots = {0, 1}; V rev = {0, 1}; int base = 1, max_base = -1; void init() { int mod = D::get_mod(); int tmp = mod - 1; max_base = 0; while (tmp % 2 == 0) { tmp /= 2; max_base++; } root = 2; while (true) { if (root.pow(1 << max_base).v == 1) { if (root.pow(1 << (max_base - 1)).v != 1) { break; } } root++; } } void ensure_base(int nbase) { if (max_base == -1) init(); if (nbase <= base) return; assert(nbase <= max_base); rev.resize(1 << nbase); for (int i = 0; i < (1 << nbase); ++i) { rev[i] = (rev[i >> 1] >> 1) + ((i & 1) << (nbase - 1)); } roots.resize(1 << nbase); while (base < nbase) { D z = root.pow(1 << (max_base - 1 - base)); for (int i = 1 << (base - 1); i < (1 << base); ++i) { roots[i << 1] = roots[i]; roots[(i << 1) + 1] = roots[i] * z; } ++base; } } void ntt(V& a, bool inv = false) { int n = a.size(); // assert((n & (n - 1)) == 0); int zeros = __builtin_ctz(n); ensure_base(zeros); int shift = base - zeros; for (int i = 0; i < n; i++) { if (i < (rev[i] >> shift)) { swap(a[i], a[rev[i] >> shift]); } } for (int k = 1; k < n; k <<= 1) { for (int i = 0; i < n; i += 2 * k) { for (int j = 0; j < k; j++) { D x = a[i + j]; D y = a[i + j + k] * roots[j + k]; a[i + j] = x + y; a[i + j + k] = x - y; } } } int v = D(n).inv().v; if (inv) { reverse(a.begin() + 1, a.end()); for (int i = 0; i < n; i++) { a[i] *= v; } } } V mul(V a, V b) { if (a.size() == 0 && b.size() == 0) return {}; int s = a.size() + b.size() - 1; int nbase = 1; while ((1 << nbase) < s) nbase++; int sz = 1 << nbase; if (sz <= 16) { V ret(s); for (int i = 0; i < a.size(); i++) { for (int j = 0; j < b.size(); j++) ret[i + j] += a[i] * b[j]; } return ret; } a.resize(sz); b.resize(sz); ntt(a); ntt(b); for (int i = 0; i < sz; i++) { a[i] *= b[i]; } ntt(a, true); a.resize(s); return a; } }; // T : modint template void ntt_2d(VV& a, bool rev) { if (a.size() == 0 || a[0].size() == 0) return; int h = a.size(), w = a[0].size(); NumberTheoreticTransform fft; fft.init(); for (auto& v : a) { fft.ntt(v, rev); } rep(j, w) { V vh(h); rep(i, h) { vh[i] = a[i][j]; } fft.ntt(vh, rev); rep(i, h) { a[i][j] = vh[i]; } } } NumberTheoreticTransform ntt; void slv() { ntt.init(); int H, W; cin >> H >> W; V v1(H + 1), v2(W + 1); for (int i = 1; i <= H; ++i) { v1[i] = comb(i, H - i) * ifact[i]; } for (int i = 1; i <= W; ++i) { v2[i] = comb(i, W - i) * ifact[i]; } auto v3 = ntt.mul(v1, v2); Mint ans; for (int i = 1; i < SZ(v3); ++i) { ans += v3[i] * fact[i]; } show(ans); } int main() { int cases = 1; // cin >> cases; rep(i, cases) slv(); return 0; }