#include <iostream>
#include <cmath>
#include <algorithm>
#include <stdio.h>
#include <cstring>
#include <string>
#include <cstdlib>
#include <vector>
#include <bitset>
#include <map>
#include <chrono>
#include <functional>
#include <unordered_set>
#include <unordered_map>
#include <numeric>
#include <queue>
#include <ctime>
#include <stack>
#include <set>
#include <list>
#include <deque>
#include <iomanip>
#include <sstream>
#include <fstream>
#include <stdarg.h>
#include <utility>

using namespace std;

#define pb push_back
#define mp make_pair
#define ll long long
#define ull unisgned long long
#define ld long double
#define all(a) a.begin(), a.end()
#define SORT(a) sort(all(a))
#define pii pair<int, int>
#define tii triple<int, int, int>
#define e 1e-7
#define PI acos(-1)
#define sz(a) (int)(a.size())
#define inf 1e17
#define vi vector<int>
#define F first
#define S second
#define rng(x) for(int _ = 0; _ < (x); _++)
#define rngi(i, x) for(int i = 0; i < (x); i++)
#define rngsi(s, i, x) for(int i = (s); i <(x); i++)
#define int long long
#define problem ""

template<typename A, typename B, typename C>
struct triple{
    A X;
    B Y;
    C Z;
    triple(A a = 0, B b = 0, C c = 0) :X(a), Y(b), Z(c) {}
};
template<typename A, typename B, typename C>
triple<A, B, C> make_triple(A a = 0, B b = 0, C c = 0){
    return triple<A, B, C>(a, b, c);
}
template<typename A, typename B, typename C>
bool operator<(const triple<A, B, C>& a, const triple<A, B, C>& b){
    if (a.X != b.X)
        return a.X < b.X;
    if (a.Y != b.Y)
        return a.Y < b.Y;
    return a.Z < b.Z;
}
template<typename T, typename SS>
ostream& operator<<(ostream& ofs, const pair<T, SS>& p){
    ofs << "( " << p.F << " , " << p.S << " )";
    return ofs;
}
template<typename T>
void print(T a){
    for (auto i : a)
        cout << i << ' ';
    cout << '\n';
}
template<typename T>
T max(T a, T b, T c){
    return max(a, max(b, c));
}
template<typename T>
T min(T a, T b, T c){
    return min(a, min(b, c));
}
template<typename T, typename D>
D min(T a){
    return *min_element(all(a));
}
template<typename T, typename D>
D max(T a){
    return *max_element(all(a));
}
struct custom_hash{
    static uint64_t splitmix64(uint64_t x){
        x += 0x9e3779b97f4a7c15;
        x = (x ^ (x >> 30)) * 0xbf58476d1ce4e5b9;
        x = (x ^ (x >> 27)) * 0x94d049bb133111eb;
        return x ^ (x >> 31);
    }

    size_t operator()(uint64_t x) const{
        static const uint64_t FIXED_RANDOM = chrono::steady_clock::now().time_since_epoch().count();
        return splitmix64(x + FIXED_RANDOM);
    }
};
const int mod = 998244353;
int dp[3001][3001];
void solve(){
    int a,b,c,d;
    cin>>a>>b>>c>>d;
    dp[a][b]=1;
    for(ll i=a+1;i<=c;i++)dp[i][b]=(i*dp[i][b-1]+(b)*dp[i-1][b]-(i-1)*(b-1)*dp[i-1][b-1]%mod+mod)%mod;
    for(ll j=b+1;j<=d;j++)dp[a][j]=((a)*dp[a][j-1]+(j)*dp[a-1][j]-(a-1)*(j-1)*dp[a-1][j-1]%mod+mod)%mod;
    for(ll i=a+1;i<=c;i++){
        for(ll j=b+1;j<=d;j++){
            dp[i][j]=(i*dp[i][j-1]%mod+j*dp[i-1][j]%mod-(i-1)*(j-1)*dp[i-1][j-1]%mod+mod)%mod;
        }
    }
    cout<<dp[c][d];
};
signed main()
{
    if(0){
        freopen(problem".in", "r", stdin);
        freopen(problem".out", "w", stdout);
    }
    srand(time(NULL));
    cin.tie(0);
    cout.tie(0);
    ios_base::sync_with_stdio(false);
    int t = 1; //cin >> t;
    rng(t) solve();
}


Measured memory_bytes: 73812