#include <bits/stdc++.h>

#define EQ(a,b) (fabs(a - b) <= fabs(a + b)*EPS)

using namespace std;



int main()
{
    ios::sync_with_stdio(false);

    int A, B, K, C;
    cin >> A >> B >> K >> C;

    if(C == A || C == B)
    {
        cout << ((K * int(pow(2, K-1))) %  1000000007) << endl;
    }
    else
    {
        cout << 0 << endl;
    }
    
        
    return 0;
}