package com.company;

import java.util.Scanner;

public class Main {

    static int fact(int a) {
        int ans = 1;
        for (int i = 1; i <= a; i++) ans *= i;
        return ans;
    }

    static int[][] copyArr(int[][] arr, int n, int m) {
        int newArr[][] = new int [n][m];
        for (int i = 0;i < n; i++) {
            for (int j = 0; j < m; j++) {
                newArr[i][j] = arr[i][j];
            }
        }
        return newArr;
    }

    static int algo(int[][] arr, int w, int b, int m, int n) {
        if (w == 0 && b == 0) return 1;
        int ans = 0;
        if (w != 0) {
            for (int i = 0; i < m; i++) {
                for (int j = 0; j < n; j++) {
                    int[][] copied = copyArr(arr, m, n);
                    if (copied[i][j] != 'w') {
                        copied[i][j] = 'w';
                        ans += algo(copied, w - 1, b, m, n);
                    }
                }
            }
        }
        else {
            boolean available;

            for (int i = 0; i < m; i++) {
                for (int j = 0; j < n; j++) {
                    available = true;
                    int[][] copied = copyArr(arr, m, n);


                    for (int k = 0; k < n; k++)
                        if (copied[i][k] == 'w') available = false;

                    for (int k = 0; k < m; k++)
                        if (copied[k][j] == 'w') available = false;

                    if ((copied[i][j] == 0) && available) {
                        copied[i][j] = 'b';
                        ans += algo(copied, w, b - 1, m, n);
                    }
                }
            }
        }
        return ans;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);

        int m = in.nextInt(), n = in.nextInt();
        int arr[][] = new int[m][n];

        for (int i = 0; i < m; i++) for (int j = 0; j < n; j++) arr[i][j] = 0;

        int w = in.nextInt(), b = in.nextInt();

        System.out.println(algo(arr, w, b, m, n) / (fact(w) * fact(b)));
    }
}