#include <bits/stdc++.h>

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

using namespace std;

long long int modNum = 1000000007;

long long int customPow(int b, int p)
{
    long long int ret = b;
    for(int i = 1; i < p; i++)
        ret = (ret << 1) % modNum;

    return ret;
}

int main()
{


    ios::sync_with_stdio(false);

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


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