import java.io.*;
import java.util.*;
import java.util.stream.*;

public class Main {
    static final int MOD = 998244353;
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int x = sc.nextInt();
        int y = sc.nextInt();
        int z = sc.nextInt();
        int w = sc.nextInt();
        long ans;
        if (w == 0) {
            ans = fact(x + y - z - 1) * fact(x) % MOD * pow(fact(x - z) * fact(z) % MOD, MOD - 2) % MOD * y % MOD;
        } else {
            ans = fact(x + y - w - 1) * fact(y) % MOD * pow(fact(y - w) * fact(w) % MOD, MOD - 2) % MOD * x % MOD;
        }
        System.out.println(ans);
    }
    
    static long pow(long x, int p) {
        if (p == 0) {
            return 1;
        } else if (p % 2 == 0) {
            return pow(x * x % MOD, p / 2);
        } else {
            return pow(x, p - 1) * x % MOD;
        }
    }
    
    static long fact(int x) {
        if (x == 0) {
            return 1;
        } else {
            return fact(x - 1) * x % MOD;
        }
    }
}
class Utilities {
    static String arrayToLineString(Object[] arr) {
        return Arrays.stream(arr).map(x -> x.toString()).collect(Collectors.joining("\n"));
    }
    
    static String arrayToLineString(int[] arr) {
        return String.join("\n", Arrays.stream(arr).mapToObj(String::valueOf).toArray(String[]::new));
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public int[] nextIntArray() throws Exception {
        return Stream.of(br.readLine().split(" ")).mapToInt(Integer::parseInt).toArray();
    }
    
    public String next() throws Exception {
        while (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
    
}