Test

import java.math.BigInteger;
import java.util.Scanner;

public class test2 {

    public static void main(String[] args){

        Scanner input = new Scanner(System.in);
        BigInteger FirstNumber = input.nextBigInteger();
        BigInteger SecondNumber = input.nextBigInteger();
        BigInteger ThirdNumber = input.nextBigInteger();
        int n = input.nextInt();

        BigInteger[] array = new BigInteger[n];
        array[0].add(FirstNumber);
        array[1].add(SecondNumber);
        array[2].add(ThirdNumber);

        for (int i = 0; i < n - 3; i++) {
            array[3] = array[0].add(array[1]).add(array[2]);
            array[0] = array[1];
            array[1] = array[2];
            array[2] = array[3];
        }
        System.out.println(array[3]);
    }
}