#include <bits/stdc++.h>
using namespace std;
//ios_base::sync_with_stdio(false);

int main() {
	long long A, B, C, K;
	cin >> A >> B >> K >> C;
	if(C != A && C != B) {
		cout << 0 << endl;
	}
	else if(C == A && C == B) {
		cout << K << endl;
	}
	else {
		long long res = 1;
		for(int i = 0; i < K-1; i++) {
			res = (res * 2) % 1000000007;
		}
		cout << (K*res)%1000000007 << endl;
	}

	return 0;
}