#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)
    {
        if (a == b)
            cout << k << endl;
        else
        {
            int res = k;
            for (int i = 0; i < k - 1; i++)
            {
                res *= 2;
                res %= 1000000007;
            }
            cout << res << endl;
        }
    }
    else
        cout << 0 << endl;

    return 0;
}