#include <iostream>
#include <cmath>
using namespace std;

long long myPow(int x, int n)
{
    long long out=1;
    for(int i = 0; i < n; i++)
    {
        out*=x;
        out%=1000000007;
    }
    return out;

}

int main()
{
    long long a,b,k,c, out = 0;
    cin>>a>>b>>k>>c;
    if(a==c || b==c)
    {
        out = ((myPow(2, k-1)*k));
    }
    cout<<out<<endl;
    return 0;
}