/*
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 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package beerbarrels;

import java.util.Scanner;

/**
 *
 * @author boban3
 */
public class Main {

    public static int a, b, k, c, vysledok;
    
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);        
        
        while (sc.hasNextLine()) {            
            
            String[] riadok = sc.nextLine().split(" ");
            
            a = Integer.parseInt(riadok[0]);
            b = Integer.parseInt(riadok[1]);
            k = Integer.parseInt(riadok[2]);
            c = Integer.parseInt(riadok[3]);
            vysledok = 0;
                       
            if (a != c && b != c) {
                System.out.println("0");
                continue;
            }
            
            if (a == b) {
                System.out.println(k);
                continue;
            }      
            
            if (k == 1) {
                System.out.println("1");
                continue;
            }
            
            long vysledok = 1;
            for (int i = k - 1; i >= 1; i--) {
                vysledok *= 2;
                vysledok %= 1000000007;
            }
            vysledok *= k;
            
                        
            System.out.println(vysledok % 1000000007);
        }
    }
    
}