#include <iostream>

int MOD = 1e9 + 7;

using namespace std;

int main(void) {
	int a,b,k,c;
	cin >> a >> b >> k >> c;
	if ((c!= a && c != b) || k == 0) cout << 0 << endl;
	else {
		int pow = k;
		for (int i = 0; i < k - 1; i++) {
			pow = (pow << 1) % MOD;
		}
		cout << pow << endl;
	}
	return 0;
}