#include <cstdio>

using namespace std;

long constXYZ = 1000000007;

long myPow(int K)
{
	long x = K;
	for (int i = 1; i < K; i++)
		x = (x * 2) % constXYZ;

	return x;
}

int main()
{
	int A, B, K, C;	

	while (scanf("%d %d %d %d", &A, &B, &K, &C) != EOF)
	{
		if (K == 0)
		{
			printf("0\n");
			break;
		}

		if (C != A && C != B)
		{
			printf("0\n");
			break;
		}

		if (A == B)
		{
			printf("%d\n", K);
			break;
		}

		printf("%ld\n", myPow(K));
	}

	return 0;
}