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

using namespace std;

double numOfC(int k, int a, int b)
{

    double result = 0;
    double pocetCisel = pow(2,k);
    for(int i = 0;i < k;i++)
    {
        result += pocetCisel/2;
    }
    if(a==b)
    {
        return 2 * result;
    }
    return result;
}


int main()
{
    int a,b,c,k;

    cin >> a;
    cin >> b;
    cin >> k;
    cin >> c;

    cout << numOfC(k,a,b);
    //cout << numOfC2(1000) << endl;

    //cout << pow(2,302);

    return 0;
}