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

using namespace std;

int main()
{
    int A=0,B=0,K,C;
    cin >> A >> B >> K >> C;
    if(A != 0 || B != 0 || K != 0 || C != 0)
        cout << (pow(2,K)*K)/2;
    return 0;
}