import java.util.Scanner;

public class Barrels {

    public static int A;
    public static int B;
    public static int L;
    public static int F;

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

        while (sc.hasNextInt()) {
            A = sc.nextInt();
            B = sc.nextInt();

            L = sc.nextInt();
            F = sc.nextInt();

            if (F == A || F == B) {
                long sum = 0;
                for (long i = 1; i <= L; i++) {
                    sum += (i * (factorial(L)  / (factorial(i) * factorial(L - i) ))) % 1000000007;
                }
                System.out.println(sum);
            } else {
                System.out.println(0);
            }

        }
    }

    public static long factorial(long n) {
        if(n == 0) return 1;
        
        long sum = n;
        for (long i = n - 1; i > 0; i--) {
            sum = (sum * i) % 1000000007;
        }

        return sum;
    }

}