#include<bits/stdc++.h>

template <int MOD_> struct modnum {
	static constexpr int MOD = MOD_;
	static_assert(MOD_ > 0, "MOD must be positive");

private:
	using ll = long long;

	int v;

	static int minv(int a, int m) {
		a %= m;
		assert(a);
		return a == 1 ? 1 : int(m - ll(minv(m, a)) * ll(m) / a);
	}

public:

	modnum() : v(0) {}
	modnum(ll v_) : v(int(v_ % MOD)) { if (v < 0) v += MOD; }
	explicit operator int() const { return v; }
	friend std::ostream& operator << (std::ostream& out, const modnum& n) { return out << int(n); }
	friend std::istream& operator >> (std::istream& in, modnum& n) { ll v_; in >> v_; n = modnum(v_); return in; }

	friend bool operator == (const modnum& a, const modnum& b) { return a.v == b.v; }
	friend bool operator != (const modnum& a, const modnum& b) { return a.v != b.v; }

	modnum inv() const {
		modnum res;
		res.v = minv(v, MOD);
		return res;
	}
	friend modnum inv(const modnum& m) { return m.inv(); }
	modnum neg() const {
		modnum res;
		res.v = v ? MOD-v : 0;
		return res;
	}
	friend modnum neg(const modnum& m) { return m.neg(); }

	modnum operator- () const {
		return neg();
	}
	modnum operator+ () const {
		return modnum(*this);
	}

	modnum& operator ++ () {
		v ++;
		if (v == MOD) v = 0;
		return *this;
	}
	modnum& operator -- () {
		if (v == 0) v = MOD;
		v --;
		return *this;
	}
	modnum& operator += (const modnum& o) {
		v += o.v;
		if (v >= MOD) v -= MOD;
		return *this;
	}
	modnum& operator -= (const modnum& o) {
		v -= o.v;
		if (v < 0) v += MOD;
		return *this;
	}
	modnum& operator *= (const modnum& o) {
		v = int(ll(v) * ll(o.v) % MOD);
		return *this;
	}
	modnum& operator /= (const modnum& o) {
		return *this *= o.inv();
	}

	friend modnum operator ++ (modnum& a, int) { modnum r = a; ++a; return r; }
	friend modnum operator -- (modnum& a, int) { modnum r = a; --a; return r; }
	friend modnum operator + (const modnum& a, const modnum& b) { return modnum(a) += b; }
	friend modnum operator - (const modnum& a, const modnum& b) { return modnum(a) -= b; }
	friend modnum operator * (const modnum& a, const modnum& b) { return modnum(a) *= b; }
	friend modnum operator / (const modnum& a, const modnum& b) { return modnum(a) /= b; }
};

template <typename T, int NDIMS> struct tensor_view {
	static_assert(NDIMS >= 0);

protected:
	std::array<int, NDIMS> shape;
	std::array<int, NDIMS> strides;
	T* data;

	tensor_view(std::array<int, NDIMS> shape_, std::array<int, NDIMS> strides_, T* data_) : shape(shape_), strides(strides_), data(data_) {}

public:
	tensor_view() : shape{0}, strides{0}, data(nullptr) {}

protected:
	int flatten_index(std::array<int, NDIMS> idx) const {
		int res = 0;
		for (int i = 0; i < NDIMS; i++) { res += idx[i] * strides[i]; }
		return res;
	}
	int flatten_index_checked(std::array<int, NDIMS> idx) const {
		int res = 0;
		for (int i = 0; i < NDIMS; i++) {
			assert(0 <= idx[i] && idx[i] < shape[i]);
			res += idx[i] * strides[i];
		}
		return res;
	}

public:
	T& operator[] (std::array<int, NDIMS> idx) const {
		return data[flatten_index(idx)];
	}
	T& at(std::array<int, NDIMS> idx) const {
		return data[flatten_index_checked(idx)];
	}

	template <int D = NDIMS>
	std::enable_if_t<(0 < D), tensor_view<T, NDIMS-1>> operator[] (int idx) const {
		std::array<int, NDIMS-1> nshape; std::copy(shape.begin()+1, shape.end(), nshape.begin());
		std::array<int, NDIMS-1> nstrides; std::copy(strides.begin()+1, strides.end(), nstrides.begin());
		T* ndata = data + (strides[0] * idx);
		return tensor_view<T, NDIMS-1>(nshape, nstrides, ndata);
	}
	template <int D = NDIMS>
	std::enable_if_t<(0 < D), tensor_view<T, NDIMS-1>> at(int idx) const {
		assert(0 <= idx && idx < shape[0]);
		return operator[](idx);
	}

	template <int D = NDIMS>
	std::enable_if_t<(0 == D), T&> operator * () const {
		return *data;
	}

	template <typename U, int D> friend struct tensor_view;
	template <typename U, int D> friend struct tensor;
};

template <typename T, int NDIMS> struct tensor {
protected:
	std::array<int, NDIMS> shape;
	std::array<int, NDIMS> strides;
	int len;
	T* data;

public:
	tensor() : shape{0}, strides{0}, len(0), data(nullptr) {}

	explicit tensor(std::array<int, NDIMS> shape_, const T& t = T()) {
		shape = shape_;
		strides[NDIMS-1] = 1;
		for (int i = NDIMS-1; i > 0; i--) {
			strides[i-1] = strides[i] * shape[i];
		}
		len = strides[0] * shape[0];
		data = new T[len];
		std::fill(data, data + len, t);
	}

	tensor(const tensor& o) : shape(o.shape), strides(o.strides), len(o.len), data(new T[len]) {
		for (int i = 0; i < len; i++) {
			data[i] = o.data[i];
		}
	}

	tensor& operator=(tensor&& o) noexcept {
		using std::swap;
		swap(shape, o.shape);
		swap(strides, o.strides);
		swap(len, o.len);
		swap(data, o.data);
	}
	tensor(tensor&& o) : tensor() {
		*this = std::move(o);
	}
	tensor& operator=(const tensor& o) {
		return *this = tensor(o);
	}
	~tensor() { delete[] data; }

	using view_t = tensor_view<T, NDIMS>;
	view_t view() {
		return tensor_view<T, NDIMS>(shape, strides, data);
	}
	operator view_t() {
		return view();
	}

	using const_view_t = tensor_view<const T, NDIMS>;
	const_view_t view() const {
		return tensor_view<const T, NDIMS>(shape, strides, data);
	}
	operator const_view_t() const {
		return view();
	}

	T& operator[] (std::array<int, NDIMS> idx) { return view()[idx]; }
	T& at(std::array<int, NDIMS> idx) { return view().at(idx); }
	const T& operator[] (std::array<int, NDIMS> idx) const { return view()[idx]; }
	const T& at(std::array<int, NDIMS> idx) const { return view().at(idx); }

	template <int D = NDIMS>
	std::enable_if_t<(0 < D), tensor_view<T, NDIMS-1>> operator[] (int idx) {
		return view()[idx];
	}
	template <int D = NDIMS>
	std::enable_if_t<(0 < D), tensor_view<T, NDIMS-1>> at(int idx) {
		return view().at(idx);
	}

	template <int D = NDIMS>
	std::enable_if_t<(0 < D), tensor_view<const T, NDIMS-1>> operator[] (int idx) const {
		return view()[idx];
	}
	template <int D = NDIMS>
	std::enable_if_t<(0 < D), tensor_view<const T, NDIMS-1>> at(int idx) const {
		return view().at(idx);
	}

	template <int D = NDIMS>
	std::enable_if_t<(0 == D), T&> operator * () {
		return *view();
	}
	template <int D = NDIMS>
	std::enable_if_t<(0 == D), const T&> operator * () const {
		return *view();
	}
};

int main() {
	using namespace std;
	ios_base::sync_with_stdio(false), cin.tie(nullptr);

	using num = modnum<998244353>;

	int A, B, C, D; cin >> A >> B >> C >> D;
	assert(A <= C && B <= D);
	tensor<array<num, 2>, 2> dp({C+1, D+1});
	dp[{A,B}][1] ++;
	for (int i = A; i <= C; i++) {
		for (int j = B; j <= D; j++) {
			if (i < C) {
				dp[{i+1, j}][0] += dp[{i,j}][0] * j;
				dp[{i+1, j}][0] += dp[{i,j}][1] * j;
			}
			if (j < D) {
				dp[{i, j+1}][1] += dp[{i,j}][0];
				dp[{i, j+1}][1] += dp[{i,j}][1] * i;
			}
		}
	}
	cout << dp[{C,D}][0] + dp[{C,D}][1] << '\n';

	return 0;
}


Measured memory_bytes: 73532