#include  <iostream>
using namespace std;

int main()
{
    int a,b,c,k;
    cin  >> a >> b >> k >> c;
    if(c != a && c != b)
        cout <<  0 << endl;
    else{
        int ret = k;
        for(int i=1; i<k; i++)
        {
            ret *= 2;
            ret %= 1000000007;
        }
        cout << ret << endl;
    }

}