code

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

public class Main {
    static long mod = 1000000000+7;
    static int n1;
    static int n2;
    static int noOfStudent;



     public static long optimized(int i , int g, int boysPlaced, int girlsPlaced, long[][][][] dp){
        if(i == noOfStudent+1){
            return 1;
        }

        long ways = 0;
        if(dp[i][g][boysPlaced][girlsPlaced]  != -1){
            return dp[i][g][boysPlaced][girlsPlaced];
        }

        int b = noOfStudent - (i-1);
        b = b-g;



        // place a boy
        if(b > 0 && boysPlaced < n1){
            ways += optimized(i+1,g,boysPlaced+1,0,dp)%mod;
        }



        // place a girl
        if(g > 0 && girlsPlaced < n2){
            ways  += optimized(i+1,g-1,0,girlsPlaced+1,dp)%mod;
        }


        return dp[i][g][boysPlaced][girlsPlaced] = ways;


    }



    public static void main(String args[]) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] in = br.readLine().trim().split(" ");

        int b = Integer.parseInt(in[0]);
        int g = Integer.parseInt(in[1]);

        n1 = Integer.parseInt(in[2]);
        n2 = Integer.parseInt(in[3]);
        noOfStudent = b+g;

        long[][][][] dp = new long[noOfStudent+1][g+1][21][21];



        for(int i  = 0;  i < dp.length; i++){
            for(int j = 0; j < dp[i].length; j++){
                for(int k = 0; k < dp[i][j].length; k++){
                    Arrays.fill(dp[i][j][k],-1);
                }
            }
        }






       System.out.println(optimized(1,g,0,0,dp));

    }
}