#include <iostream>
#include <cstdlib>
#include <math.h>

using namespace std;

int main()
{
    int A,B,C,K;
    unsigned long long Ans,x;

    cin >> A >> B >> K >> C;

    if(C == A && C == B)
    {
        Ans = K;
    }
    else if(C == A || C == B)
    {
        x = pow(2,K);
        Ans = (x*K)/2;
    }

    Ans = Ans%1000000007;
    cout << Ans;
    return 0;
}