#include<vector>
#include<iostream>

using namespace std;

int fact(int num){
	int sum = 1;
	for(int i = 1; i <= num; ++i){
		sum *= i;
		sum %= 1000000007;
	}

	return sum;
}

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

	if(c == a || c == b){
		int sum = k;
		
		for(int i = k - 1; i > 0; --i){
			sum += i * (fact(k) / (fact(k - i) * fact(i)));
			sum %= 1000000007;
		}

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

	return 0;
}