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

public class Barrels {

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



        int vysledok = (int) (((Math.pow(2,k-1)*k))%1000000007);
        if(c != a || c != b){
            System.out.println("chyba");
        }
        else{
            System.out.println(vysledok);
        }

    }
}