import java.util.ArrayList;
import java.util.Scanner;

public class Barrels {

    public static void main(String[] args) {
        int a,b,c,k,vysledok;
        Scanner sken = new Scanner(System.in);
        a = sken.nextInt();
        b = sken.nextInt();
        k = sken.nextInt();
        c = sken.nextInt();
        vysledok = 0;

        if(a != b){
            vysledok = (int) (((Math.pow(2,k-1)*k))%1000000007);
        }
        if(a == b){
            vysledok = (int) ((((Math.pow(2,k)*k)))%1000000007);
        }
        if(!(c == a || c == b)){
            vysledok = 0;
        }

        System.out.println(vysledok);
    }
}