import java.util.*; 
import java.io.*;
import java.math.*;

class Main{
    // Const //
    static final int MOD7 = 1000000007;
    static final int MOD9 = 998244353 ;
    static final int  inf = (1  << 30);
    static final long lnf = (1L << 60);
    final String yes = "Yes";
    final String no  = "No" ;
    final int [] dy4 = {-1,0,1,0};
    final int [] dx4 = {0,1,0,-1};
    final int [] dy8 = {-1,-1,-1,0,1,1,1,0};
    final int [] dx8 = {-1,0,1,1,1,0,-1,-1};
    // Variables //

    // Solve //
    void solve() {   
        int x = in.nextInt() , y = in.nextInt() , z = in.nextInt() , w = in.nextInt();
        int a = x - z , b = y - w ;
        MC mc = new MC(MOD9);
        long ans = 1 ;
        if(z == 0) {
            ans *= x;
            ans %= MOD9;
            ans *= mc.combination(x - 1, a - 1);
            ans %= MOD9;
            ans *= mc.combination(x, b);
            ans %= MOD9;
            ans *= mc.factorial(a + b - 1);
            ans %= MOD9;
        }
        if(w == 0) {
            ans *= y;
            ans %= MOD9;
            ans *= mc.combination(y - 1, b - 1);
            ans %= MOD9;
            ans *= mc.combination(x, a);
            ans %= MOD9;
            ans *= mc.factorial(a + b - 1);
            ans %= MOD9;
        }
        out.println(ans == 1 ? 0 : ans % MOD9);
    }
    // Function //

    // Main //
    public static void main(String[] args) {
        new Main().solve();
        out.flush();
    }
    // Interface //
    static PrintWriter out = new PrintWriter(System.out);
    static In in = new In();
    static Debug debug = new Debug();
}
// Class //
class MC {
    private final int mod;
    public MC(final int mod) {
      this.mod = mod;
    }
 
    public long mod(long x) {
      x %= mod;
      if (x < 0) {
        x += mod;
      }
      return x;
    }
 
    public long add(final long a, final long b) {
      return mod(a + b);
    }
 
    public long mul(final long a, final long b) {
      return mod(a * b);
    }
 
    public long div(final long numerator, final long denominator) {
      return mod(numerator * inverse(denominator));
    }
 
    public long power(long base, long exp) {
      long ret = 1;
      base %= mod;
      while (exp > 0) {
        if ((exp & 1) == 1) {
          ret = mul(ret, base);
        }
        base = mul(base, base);
        exp >>= 1;
      }
      return ret;
    }
 
    public long inverse(final long x) {
      return power(x, mod - 2);
    }
 
    public long factorial(final int n) {
      return product(1, n);
    }
 
    public long product(final int start, final int end) {
      long result = 1;
      for (int i = start; i <= end; i++) {
        result *= i;
        result %= mod;
      }
      return result;
    }
 
    public long combination(final int n, int r) {
      if (r > n) {
        return 0;
      }
      return div(product(n - r + 1, n), factorial(r));
    }
}
class Pair<T extends Comparable<T>, U extends Comparable<U>> implements Comparable<Pair<T, U>> {

    private final T first;
    private final U second;

    Pair(T first, U second) {
        this.first = first;
        this.second = second;
    }

    T first() {
        return first;
    }

    U second() {
        return second;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Pair<?, ?> pair = (Pair<?, ?>) o;
        return Objects.equals(first, pair.first) && Objects.equals(second, pair.second);
    }

    @Override
    public int hashCode() {
        return Objects.hash(first, second);
    }

    @Override
    public int compareTo(Pair<T, U> other) {
        T f  = this.first  , F  = other.first;
        U s  = this.second , S  = other.second;
        int First_Result  = f.compareTo(F);
        int Second_Result = s.compareTo(S);
        return First_Result == 0 ? Second_Result : First_Result ;
    }

    @Override
    public String toString() {
        return "(" + this.first + " , " + this.second + ")";
    }
}

class Triple<T extends Comparable<T>, U extends Comparable<U>, V extends Comparable<V>> implements Comparable<Triple<T, U, V>> {
    
    private final T first;
    private final U second;
    private final V third;

    Triple(T first, U second, V third) {
        this.first = first;
        this.second = second;
        this.third = third;
    }

    T first() {
        return first;
    }

    U second() {
        return second;
    }

    V third() {
        return third;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Triple<?, ?, ?> triple = (Triple<?, ?, ?>) o;
        return Objects.equals(first, triple.first) 
            && Objects.equals(second, triple.second)
            && Objects.equals(third, triple.third) ;
    }


    @Override
    public int hashCode() {
        return Objects.hash(first, second, third);
    }

    @Override
    public int compareTo(Triple<T, U, V> other) {
        T f  = this.first  , F  = other.first;
        U s  = this.second , S  = other.second;
        V t  = this.third  , T  = other.third;
        int First_Result  = f.compareTo(F);
        int Second_Result = s.compareTo(S);
        int Third_Result  = t.compareTo(T);
        return Second_Result == 0 ? (First_Result == 0 ? Third_Result : First_Result ) : Second_Result;
    }

    @Override
    public String toString() {
        return "(" + this.first + " , " + this.second + " , " + this.third + ")";
    }
}
// Debug //
class Debug {

    private PrintWriter out = new PrintWriter(System.out);

    public void display(int [] a) { out.println(Arrays.toString(a)); fl();}
    public void display(long [] a) { out.println(Arrays.toString(a)); fl();}
    public void display(double [] a) { out.println(Arrays.toString(a)); fl();}
    public void display(String [] a) { out.println(Arrays.toString(a)); fl();}
    public void display(char [] a) { out.println(Arrays.toString(a)); fl();}
    public void display(boolean [] a) { char [] c = conv(a); display(c); fl();}
    public void display(int [][] a) { for(int i = 0 ; i < a.length ; i ++ ) out.println(Arrays.toString(a[i])); fl();}
    public void display(long [][] a) { for(int i = 0 ; i < a.length ; i ++ ) out.println(Arrays.toString(a[i])); fl();}
    public void display(double [][] a) { for(int i = 0 ; i < a.length ; i ++ ) out.println(Arrays.toString(a[i])); fl();}
    public void display(String [][] a) { for(int i = 0 ; i < a.length ; i ++ ) out.println(Arrays.toString(a[i])); fl();}
    public void display(char [][] a) { for(int i = 0 ; i < a.length ; i ++ ) out.println(Arrays.toString(a[i])); fl();}
    public void display(boolean [][] a) { char [][] c = new char [a.length][a[0].length] ; for(int i = 0 ; i < a.length ; i ++ ) c[i] = conv(a[i]) ; display(c); fl();}
    private char [] conv(boolean [] a) { char [] c = new char[a.length] ; for(int i = 0 ; i < a.length ; i ++ ) c[i] = a[i] ? 'O' : 'X' ; return c ; }
    private void fl() { out.flush(); }
}

// Input // 
class In{

    private final InputStream in = System.in;
    private final byte[] buffer = new byte[1024];
    private int ptr = 0;
    private int buflen = 0;

    private boolean hasNextByte() {
        if (ptr < buflen) {
            return true;
        }else{
            ptr = 0;
            try {
                buflen = in.read(buffer);
            } catch (IOException e) {
                e.printStackTrace();
            }
            if (buflen <= 0) {
                return false;
            }
        }
        return true;
    }

    private int readByte() { 
        if (hasNextByte()) return buffer[ptr++]; else return -1;
    }

    private static boolean isPrintableChar(int c) { 
        return 33 <= c && c <= 126;
    }

    public boolean hasNext() { 
        while(hasNextByte() && !isPrintableChar(buffer[ptr])) {
            ptr++; 
        }
        return hasNextByte();
    }

    String next() {
        if (!hasNext()) throw new NoSuchElementException();
        StringBuilder sb = new StringBuilder();
        int b = readByte();
        while(isPrintableChar(b)) {
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }

    long nextLong() {
        if (!hasNext()) throw new NoSuchElementException();
        long n = 0;
        boolean minus = false;
        int b = readByte();
        if (b == '-') {
            minus = true;
            b = readByte();
        }
        if (b < '0' || '9' < b) {
            throw new NumberFormatException();
        }
        while(true){
            if ('0' <= b && b <= '9') {
                n *= 10;
                n += b - '0';
            }else if(b == -1 || !isPrintableChar(b)){
                return minus ? -n : n;
            }else{
                throw new NumberFormatException();
            }
            b = readByte();
        }
    }
    int nextInt() {
        long nl = nextLong();
        if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE) throw new NumberFormatException();
        return (int) nl;
    }
    double nextDouble() { 
        return Double.parseDouble(next());
    }
    char nextChar() {
        return next().charAt(0);
    }
    int [] IntArray(int n) {
        final int [] Array = new int [n];
        for(int i = 0 ; i < n ; i ++ ) {
            Array[i] = nextInt();
        }
        return Array;
    }
    int [][] IntArray(int n , int m) {
        final int [][] Array = new int [n][m];
        for(int i = 0 ; i < n ; i ++ ) {
            Array[i] = IntArray(m);
        }
        return Array;
    }   
    long [] LongArray(int n) {
        final long [] Array = new long [n];
        for(int i = 0 ; i < n ; i ++ ) {
            Array[i] = nextLong();
        }
        return Array;
    }
    long [][] LongArray(int n , int m) {
        final long [][] Array = new long [n][m];
        for(int i = 0 ; i < n ; i ++ ) {
            Array[i] = LongArray(m);
        }
        return Array;
    }
    String [] StringArray(int n) {
        final String [] Array = new String [n];
        for(int i = 0 ; i < n ; i ++ ) {
            Array[i] = next();
        }
        return Array;
    }
    char [] CharArray(int n) {
        final char [] Array = new char[n];
        for(int i = 0 ; i < n ; i ++ ) {
            Array[i] = next().charAt(0);
        }
        return Array;
    }
    char [][] CharArray(int n , int m) {
        final char [][] Array = new char [n][m];
        for(int i = 0 ; i < n ; i ++ ) {
            Array[i] = next().toCharArray();
        }
        return Array;
    }
    char [][] CharArray2(int n , int m) {
        final char [][] Array = new char [n][m];
        for(int i = 0 ; i < n ; i ++ ) {
            for(int j = 0 ; j < n ; j ++ ) {
                Array[i][j] = next().charAt(0);
            }
        }
        return Array;
    }
}