#include <iostream>

using namespace std;

int main()
{
    int a,b,c,k;
    cin >> a;
    cin >> b;
    cin >> k;
    cin >> c;
    if (c == a || c == b)
    {
        long long res = 2;
        for (int i = 0; i < k - 2; i++)
        {
            res *= 2;
            res %= 1000000007;
        }
        res *= k;
        res %= 1000000007;
        cout << res << endl;
    }
    else
        cout << 0 << endl;

    return 0;
}