#include <bits/stdc++.h>
#define endl '\n'
#define pb push_back
#define mp make_pair
#define int long long
#define INF 0x3f3f3f3f
#define Inf 1000000000000000000LL
#define F first
#define S second
using namespace std;
typedef pair<int,int>pii;
const int MOD=998244353;
int a,b,c,d;
int dp[3010][3010];//
signed main(){
	memset(dp,0,sizeof dp);
	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||j!=b){
			dp[i][j]=(dp[i-1][j]*j+dp[i][j-1]*i+MOD-dp[i-1][j-1]*(i-1)*(j-1)+MOD)%MOD;
//			cerr<<i<<' '<<j<<' '<<dp[i][j]<<endl;
			if(dp[i][j]<0)dp[i][j]+=MOD;
		}
	cout<<dp[c][d]<<endl;
	return 0;
}
