#include <bits/stdc++.h>

using namespace std;

int main (void) {
	int A, B, K, C;
	std::cin >> A >> B >> K >> C;
	if (A != C && B != C) {
		std::cout << 0 << std::endl;
		return 0;
	}
	if (A == B) {
		std::cout << K % 1000000007 << std::endl;
		return 0;
	}
	int res = K * int(pow(2, K - 1));
	std::cout << (res % 1000000007) << std::endl;
	return 0;
}