#include <bits/stdc++.h>

using namespace std;

const int N = 3e5 + 7;
const int MX = 1e9 + 7;

int main(){
	int a, b, k, c;
	cin >> a >> b >> k >> c;
	
	if(c != a && c != b){
		cout << "0\n";
		exit(0);
	}
	
	int ans = k;
	for(int i = 1; i < k; ++i)
		ans = (ans + ans) % MX;
	cout << ans << "\n";
	return 0;
}