import java.util.*;

public class Run {
    public static void main (String arg[]) {
        Scanner scan = new Scanner(System.in);
        long F0 = scan.nextLong();
        long F1 = scan.nextLong();
        long N = scan.nextLong();
        if (F0 < 0||F1 < 0||N > Math.pow(10d, 18)) System.exit(1);

        if (N==0) {
            System.out.println(F0);
            System.exit(0);
        } else {
            long tmp;
            for (int i = 0; i < N - 1; i++) {
                tmp = F1;
                F1 = F0 ^ F1;
                F0 = tmp;
            }
            System.out.println(F1);
        }
    }
}