#include <bits/stdc++.h>  // clang-format off
using Int = long long;
#define REP_(i, a_, b_, a, b, ...) for (Int i = (a), lim##i = (b); i < lim##i; i++)
#define REP(i, ...) REP_(i, __VA_ARGS__, __VA_ARGS__, 0, __VA_ARGS__)
struct SetupIO { SetupIO() { std::cin.tie(nullptr), std::ios::sync_with_stdio(false), std::cout << std::fixed << std::setprecision(13); } } setup_io;
#ifndef dump
#define dump(...)
#endif  // clang-format on

/**
 *    author:  knshnb
 *    created: Sat Jun 20 21:12:14 JST 2020
 **/

template <class T> T pow(T x, long long n, const T UNION = 1) {
    T ret = UNION;
    while (n) {
        if (n & 1) ret *= x;
        x *= x;
        n >>= 1;
    }
    return ret;
}

/// @docs src/Math/ModInt.md
template <int Mod> struct ModInt {
    int x;
    static int runtime_mod;
    static std::unordered_map<int, int> to_inv;
    // テンプレート引数が負のときは実行時ModInt
    static int mod() { return Mod < 0 ? runtime_mod : Mod; }
    static void set_runtime_mod(int mod) {
        static_assert(Mod < 0, "template parameter Mod must be negative for runtime ModInt");
        runtime_mod = mod;
        to_inv.clear();
    }
    ModInt() : x(0) {}
    ModInt(long long x_) {
        if ((x = x_ % mod() + mod()) >= mod()) x -= mod();
    }

    ModInt& operator+=(ModInt rhs) {
        if ((x += rhs.x) >= mod()) x -= mod();
        return *this;
    }
    ModInt& operator*=(ModInt rhs) {
        x = (unsigned long long)x * rhs.x % mod();
        return *this;
    }
    ModInt& operator-=(ModInt rhs) {
        if ((x -= rhs.x) < 0) x += mod();
        return *this;
    }
    ModInt& operator/=(ModInt rhs) {
        x = (unsigned long long)x * rhs.inv().x % mod();
        return *this;
    }
    ModInt operator-() const { return -x < 0 ? mod() - x : -x; }
    ModInt operator+(ModInt rhs) const { return ModInt(*this) += rhs; }
    ModInt operator*(ModInt rhs) const { return ModInt(*this) *= rhs; }
    ModInt operator-(ModInt rhs) const { return ModInt(*this) -= rhs; }
    ModInt operator/(ModInt rhs) const { return ModInt(*this) /= rhs; }
    bool operator==(ModInt rhs) const { return x == rhs.x; }
    bool operator!=(ModInt rhs) const { return x != rhs.x; }
    ModInt inv() const { return to_inv.count(this->x) ? to_inv[this->x] : (to_inv[this->x] = pow(*this, mod() - 2).x); }

    friend std::ostream& operator<<(std::ostream& s, ModInt<Mod> a) {
        s << a.x;
        return s;
    }
    friend std::istream& operator>>(std::istream& s, ModInt<Mod>& a) {
        long long tmp;
        s >> tmp;
        a = ModInt<Mod>(tmp);
        return s;
    }
    friend std::string to_string(ModInt<Mod> a) { return std::to_string(a.x); }
};
template <int Mod> std::unordered_map<int, int> ModInt<Mod>::to_inv;
template <int Mod> int ModInt<Mod>::runtime_mod;

#ifndef CALL_FROM_TEST
using mint = ModInt<998244353>;
#endif

template <class T, class S> T make_vec(S x) { return x; }
template <class T, class... Ts> auto make_vec(size_t n, Ts... ts) {
    return std::vector<decltype(make_vec<T>(ts...))>(n, make_vec<T>(ts...));
}

signed main() {
    Int A, B, C, D;
    std::cin >> A >> B >> C >> D;
    auto dp = make_vec<mint>(C + 1, D + 1, 2, 0);
    dp[A][B][0] = 1;
    dp[A][B][1] = 1;
    REP(a, 1, C + 1) {
        REP(b, 1, D + 1) {
            if (a <= A && b <= B) continue;
            dp[a][b][0] += dp[a - 1][b][0] * b;
            dp[a][b][0] += dp[a][b - 1][1] * a;
            dp[a][b][0] += dp[a - 1][b - 1][0] * (b - 1);
            dp[a][b][1] += dp[a][b - 1][1] * a;
            dp[a][b][1] += dp[a - 1][b - 1][0] * (b - 1);
        }
    }
    dump(dp);
    std::cout << dp[C][D][0] << std::endl;
}


Measured memory_bytes: 495808