/* Aa^~ kokoro ga pyonpyon suru n jaa^~
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*/
#include<bits/stdc++.h>
using namespace std;
#ifndef ONLINE_JUDGE
#define dbg(x...) do { cout << "\033[32;1m " << #x << " -> "; err(x); } while (0)
void err() { cout << "\033[39;0m" << endl; }
template<template<typename...> class T, typename t, typename... A>
void err(T<t> a, A... x) { for (auto v: a) cout << v << ' '; err(x...); }
template<typename T, typename... A>
void err(T a, A... x) { cout << a << ' '; err(x...); }
#else
#define dbg(...)
#endif
typedef long long ll;
typedef pair<int,int> pi;
typedef vector<int> vi;
template<class T> using vc=vector<T>;
template<class T> using vvc=vc<vc<T>>;
template<class T> void mkuni(vector<T>&v)
{
    sort(v.begin(),v.end());
    v.erase(unique(v.begin(),v.end()),v.end());
}
ll rand_int(ll l, ll r) //[l, r]
{
    static mt19937_64 gen(chrono::steady_clock::now().time_since_epoch().count());
    return uniform_int_distribution<ll>(l, r)(gen);
}
template<class T>
void print(T x,int suc=1)
{
    cout<<x;
    if(suc==1) cout<<'\n';
    else cout<<' ';
}
template<class T>
void print(const vector<T>&v,int suc=1)
{
    for(int i=0;i<v.size();i++)
    print(v[i],i==(int)(v.size())-1?suc:2);
}
const int mod=998244353;
const int maxn=3e3+7;
ll dp[maxn][maxn];
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int a,b,c,d;
    cin>>a>>b>>c>>d;
    dp[a][b]=1;
    for(int i=a;i<=c;i++)
    {
        for(int j=b;j<=d;j++)
        {
            if(i>a)
                dp[i][j]=(dp[i][j]+dp[i-1][j]*j)%mod;
            if(j>b)
                dp[i][j]=(dp[i][j]+dp[i][j-1]*i)%mod;
            if(i>a&&j>b)
                dp[i][j]=(dp[i][j]-dp[i-1][j-1]*(i-1)%mod*(j-1)%mod+mod)%mod;
        }
    }
    print(dp[c][d]);
}

Measured memory_bytes: 74024