import java.util.Scanner;

public class Barrels {
    public static void main(String[] args) {
        var sc = new Scanner(System.in);
        int a = sc.nextInt();
        int b = sc.nextInt();
        int k = sc.nextInt();
        int c = sc.nextInt();

        var triangle = new long[k + 1][k + 1];

        triangle[0][0] = 1;

        for (int i = 1; i < k + 1; i++) {
            triangle[i][0] = 1;
            for (int j = 1; j < i; j++) {
                triangle[i][j] = triangle[i - 1][j] + triangle[i - 1][j - 1];
            }
            triangle[i][i] = 1;
        }
        long res = 0;
        final long mod = 1000000007;

        if (c == a || c == b) {
            for (int i = 1; i < k + 1; i++) {
                res += i * triangle[k][i];
                res %= mod;
            }
        }

        System.out.println(res);
/*
        for (int i = 0; i < k + 1; i++) {
            for (int j = 0; j < k + 1; j++) {
                System.out.printf("%d ", triangle[i][j]);
            }
            System.out.println();
        }
 */

    }
}