#define _CRT_SECURE_NO_WARNINGS
#pragma GCC target("avx")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <ctime>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <memory>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
#define rep(i,n) for(int i=0;i<(lint)(n);i++)
#define REP(i,n) for(int i=1;i<=(lint)(n);i++)
#define all(V) V.begin(),V.end()
#define stackReplaceBegin(size)\
	void* p=malloc(size);\
	esp_new=(lint)p+size-1;\
	void * stack_extend_memory_ = malloc(size);\
	void * stack_extend_origin_memory_;\
	char * stack_extend_dummy_memory_ = (char*)alloca((1+(int)(((long long)stack_extend_memory_)&127))*16);\
	*stack_extend_dummy_memory_ = 0;\
	asm volatile("mov %%rsp, %%rbx\nmov %%rax, %%rsp":"=b"(stack_extend_origin_memory_):"a"((char*)stack_extend_memory_+(size)-1024));
typedef long long lint;
typedef unsigned long long ulint;
typedef std::pair<lint, lint> P;
constexpr int INF = INT_MAX/2;
constexpr lint LINF = LLONG_MAX/2;
constexpr double eps = DBL_EPSILON;
constexpr double PI=3.141592653589793238462643383279;
lint esp_new;
template<class T>
class prique :public std::priority_queue<T, std::vector<T>, std::greater<T>> {};
template <class T, class U>
inline bool chmax(T& lhs, const U& rhs) {
	if (lhs < rhs) {
		lhs = rhs;
		return 1;
	}
	return 0;
}
template <class T, class U>
inline bool chmin(T& lhs, const U& rhs) {
	if (lhs > rhs) {
		lhs = rhs;
		return 1;
	}
	return 0;
}
inline lint gcd(lint a, lint b) {
	while (b) {
		lint c = a;
		a = b; b = c % b;
	}
	return a;
}
inline lint lcm(lint a, lint b) {
	return a / gcd(a, b) * b;
}
bool isprime(lint n) {
	if (n == 1)return false;
	for (int i = 2; i * i <= n; i++) {
		if (n % i == 0)return false;
	}
	return true;
}
template<typename T>
T mypow(T a, unsigned int b) {
	if (!b)return T(1);
	if (b & 1)return mypow(a, b - 1) * a;
	T memo = mypow(a, b >> 1);
	return memo * memo;
}
lint modpow(lint a, lint b, lint m) {
	if (!b)return 1;
	if (b & 1)return modpow(a, b - 1, m) * a % m;
	lint memo = modpow(a, b >> 1, m);
	return memo * memo % m;
}
template<typename T>
void printArray(std::vector<T>& vec) {
	rep(i, vec.size() - 1)std::cout << vec[i] << " ";
	std::cout << vec.back() << std::endl;
}
template<typename T>
void printArray(T l, T r) {
	T rprev = r;
	rprev--;
	for (T i = l; i != rprev; i++) {
		std::cout << *i << " ";
	}
	std::cout << *rprev << std::endl;
}

class ModInt {
	lint value;
public:
	static const unsigned int modulo;
	ModInt() : value(0) {}
	template<typename T>
	ModInt(T value = 0) : value(value) {
		if (value < 0)value = -(lint)(-value % modulo) + modulo;
		this->value = value % modulo;
	}
	inline operator int()const { return value; }
	inline ModInt& operator+=(const ModInt& x) {
		value += x.value;
		if (value >= modulo)value -= modulo;
		return *this;
	}
	inline ModInt& operator++() {
		if (value == modulo - 1)value = 0;
		else value++;
		return *this;
	}
	inline ModInt operator-()const {
		return ModInt(0) -= *this;
	}
	inline ModInt& operator-=(const ModInt& x) {
		value -= x.value;
		if (value < 0)value += modulo;
		return *this;
	}
	inline ModInt& operator--() {
		if (value == 0)value = modulo - 1;
		else value--;
		return *this;
	}
	inline ModInt& operator*=(const ModInt& x) {
		value = value * x.value % modulo;
		return *this;
	}
	inline ModInt& operator/=(ModInt rhs) {
		int exp = modulo - 2;
		while (exp) {
			if (exp & 1)*this *= rhs;
			rhs *= rhs;
			exp >>= 1;
		}
		return *this;
	}
	template<typename T> ModInt operator+(const T& rhs)const { return ModInt(*this) += rhs; }
	template<typename T> ModInt& operator+=(const T& rhs) { return operator+=(ModInt(rhs)); }
	template<typename T> ModInt operator-(const T& rhs)const { return ModInt(*this) -= rhs; }
	template<typename T> ModInt& operator-=(const T& rhs) { return operator-=(ModInt(rhs)); }
	template<typename T> ModInt operator*(const T& rhs)const { return ModInt(*this) *= rhs; }
	template<typename T> ModInt& operator*=(const T& rhs) { return operator*=(ModInt(rhs)); }
	template<typename T> ModInt operator/(const T& rhs)const { return ModInt(*this) /= rhs; }
	template<typename T> ModInt& operator/=(const T& rhs) { return operator/=(ModInt(rhs)); }
};
std::istream& operator>>(std::istream& ist, ModInt& x) {
	lint a;
	ist >> a;
	x = a;
	return ist;
}
const unsigned int ModInt::modulo=998244353;
int a,b,c,d;
ModInt dp[6010][6010];
int main(){
	std::cin>>a>>b>>c>>d;
	if(a<b){
		std::swap(a,b);
		std::swap(c,d);
	}
	dp[a][b]=1;
	for(int i=a;i<=c;i++){
		for(int j=b;j<=d;j++){
			if(dp[i][j])continue;
			dp[i][j]=dp[i-1][j]*j+dp[i][j-1]*i-dp[i-1][j-1]*(i-1)*(j-1);
		}
	}
	std::cout<<dp[c][d]<<std::endl;
	return 0;
}


Measured memory_bytes: 285812