#include<vector>
#include<iostream>
#include<cmath>

using namespace std;

int main(){
	int a, b, c, k;
	cin >> a;
	cin >> b;
	cin >> k;
	cin >> c;

	if(c == a || c == b){
		long long i = 1;		

		for(int s = 0; s < k-1; ++s){
			i *= 2;
			i %= 1000000007; 
		}
		
		i *= k;
		i %= 1000000007;

		if(a == b)
			cout << i*2 << "\n";
		else
		cout << i << "\n";

	}else{
		cout << 0 << "\n";
	}

	return 0;
}