#include<iostream>
#include<cstdio>
#define LL long long
using namespace std;

LL mod=998244353;
LL a,b,c,d;
int dp1[3005][3005],dp2[3005][3005];
int main()
{
	LL i,j;
	cin>>a>>b>>c>>d;
	dp1[a][b]=1;
	for(i=a+1;i<=c;i++)
		dp1[i][b]=b*dp1[i-1][b]%mod;
	for(i=b+1;i<=d;i++)
		dp1[a][i]=a*dp1[a][i-1]%mod;
	for(i=a+1;i<=c;i++)
		for(j=b+1;j<=d;j++)
		{
			dp1[i][j]=(dp1[i][j-1]+dp2[i][j-1])*i%mod;
			dp2[i][j]=(dp1[i-1][j]+dp2[i-1][j]*j)%mod;
		}
	cout<<(dp1[c][d]+dp2[c][d])%mod;
	return 0;
}