#include <algorithm>
#include <complex>
#include <cstdlib>
#include <ctime>
#include <time.h>
#include <iomanip>
#include <iostream>
#include <map>
#include <math.h>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <numeric>
#include <limits>
#include <type_traits>
#include <locale>

using namespace std;
#define SAY_YES cout << "YES" << endl;
#define SAY_Yes cout << "Yes" << endl;
#define SAY_NO cout << "NO" << endl;
#define SAY_No cout << "No" << endl;
#define IFYES(TRUE_OR_FALSE)   \
    if (TRUE_OR_FALSE)         \
    {                          \
        cout << "YES" << endl; \
    }                          \
    else                       \
    {                          \
        cout << "NO" << endl;  \
    }
#define IFYes(TRUE_OR_FALSE)   \
    if (TRUE_OR_FALSE)         \
    {                          \
        cout << "Yes" << endl; \
    }                          \
    else                       \
    {                          \
        cout << "No" << endl;  \
    }
#define IFyes(TRUE_OR_FALSE)   \
    if (TRUE_OR_FALSE)         \
    {                          \
        cout << "yes" << endl; \
    }                          \
    else                       \
    {                          \
        cout << "no" << endl;  \
    }
#define DEBUG_OUTPUT_ARRAY(XXX, ONE)                            \
    for (int i = 0; i < (ONE); i++)                             \
    {                                                           \
        cout << "DEBUG: i = " << i << " -> " << XXX[i] << endl; \
    }
#define DEBUG_OUTPUT_ARRAY2(XXX, ONE, TWO)                             \
    for (int i = 0; i < (ONE); i++)                                    \
    {                                                                  \
        cout << "<<< i = " << i << " >>>" << endl;                     \
        for (int j = 0; j < (TWO); j++)                                \
        {                                                              \
            cout << "DEBUG: j = " << j << " -> " << XXX[i][j] << endl; \
        }                                                              \
    }
#define DEBUG_OUTPUT_ARRAY2_BOX(XXX, ONE, TWO) \
    for (int i = 0; i < (ONE); i++)            \
    {                                          \
        cout << i << "  ";                     \
        for (int j = 0; j < (TWO); j++)        \
        {                                      \
            cout << XXX[i][j] << " ";          \
        }                                      \
        cout << endl;                          \
    }

typedef pair<long long int, long long int> pll;
typedef pair<long long int, pll> lpll;


const long long int mod = 998244353;
const long long int INF = 1e18;
const long double PI=3.14159265358979323; 
const long long int pl=1000000;

long long int A,B,C,D;
char ch[200][200];
long long int dp[3005][3005]={};



int main(){

    cout << fixed << setprecision(18);
    cin>>A>>B>>C>>D;
    dp[A][B]=1;
    for(long long int i = A+1; i <= C; i++){
        dp[i][B]=dp[i-1][B]*B;
        dp[i][B]%=mod;
    }
    for(long long int i = B+1; i <= D; i++){
        dp[A][i]=dp[A][i-1]*A;
        dp[A][i]%=mod;
    }

    for(long long int i = A+1; i <=C; i++){
        for(long long int j = B+1; j <= D; j++){
            dp[i][j]=dp[i-1][j]*j+dp[i][j-1]*i-dp[i-1][j-1]*(i-1)*(j-1);
            dp[i][j]%=mod;
            dp[i][j]+=mod;
            dp[i][j]%=mod;
        }
    }
    cout<<dp[C][D]<<endl;
    //DEBUG_OUTPUT_ARRAY2_BOX(dp,C+1,D+1);
    
}




Measured memory_bytes: 73960