#ifndef _GLIBCXX_NO_ASSERT
#include <cassert>
#endif
#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#ifdef __GXX_EXPERIMENTAL_CXX0X__
#include <ccomplex>
#include <cfenv>
#include <cinttypes>
#include <cstdbool>
#include <cstdint>
#include <ctgmath>
#include <cwchar>
#include <cwctype>
#endif

#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>
#ifdef __GXX_EXPERIMENTAL_CXX0X__
#include <array>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#endif
size_t strlen(const char* s);
#define rep(i,n) for(long long int i=0;i<n;i++)
#define sz(x) ((int)(x).size())

using namespace std;
struct ToUpper {
	char operator()(char c) { return toupper(c); }
};
struct ToLower {
	char operator()(char c) { return tolower(c); }
};
const int N = 200010;
const int p = 998244353;
using ll = long long;

//絶対値
int ze(int a, int b) {
	if (a > b) {
		return a - b;
	}
	else {
		return b - a;
	}
}
//小さい方
long long int min(long long int a, long long int b) {
	if (a > b) {
		return b;
	}
	else {
		return a;
	}
}
//大きい方
long long int max(long long int a, long long int b) {
	if (a > b) {
		return a;
	}
	else {
		return b;
	}
}
// a^n mod 
long long modpow(long long a, long long n, long long mod) {
	long long res = 1;
	while (n > 0) {
		if (n & 1) res = res * a % mod;
		a = a * a % mod;
		n >>= 1;
	}
	return res;
}

// a^{-1} mod 
long long modinv(long long a, long long mod) {
	return modpow(a, mod - 2, mod);
}

//mod掛け算
long long mt(long long a, long long b, long long mod) {
	return (a * b) % mod;
}
long long mt(long long a, long long b, long long c, long long mod) {
	a = (a * c) % mod;
	return (a * b) % mod;
}
//メモ

/*
	memset(b, '\0', sizeof(b));
初期化*/

/*
	char s[N];
	strlen(s)
*/

/*
	if(  <  )puts("Yes");
	else puts("No");
*/

/*文字列比較
if(strcmp(name[i],s)==0)
*/

/*
	graph[a].push_back(b);//graph[a][i番目に入れた]==b
	graph[j].size()	//forで回すときとか

*/

/*添字1がa個、2がb個
  vector<vector<ll>> map(a,vector<ll>(b));
*/

int main() {
	ll a, b, c, d;
	cin >> a >> b >> c >> d;
	vector<vector<ll>> dp(3010, vector<ll>(3010));

	dp.at(a).at(b) = 1;
	rep(i, 3010) {
		if (i == 0)continue;
		rep(j, 3010) {
			if (j == 0)continue;
			if (i == a && j == b)continue;
			dp.at(i).at(j) = (mt(dp.at(i - 1).at(j), j, p) + mt(dp.at(i).at(j - 1), i, p) - mt(dp.at(i - 1).at(j - 1), i - 1, j - 1, p)+p) % p;
		}
	}
	cout << dp.at(c).at(d) << endl;
}

Measured memory_bytes: 74220