import java.util.*;

public class Run {
    public static void main (String arg[]) {
        Scanner scan = new Scanner(System.in);
        long[] F = new long[3];
        F[0] = scan.nextLong();
        F[1] = scan.nextLong();
        long N = scan.nextLong();
        if (F[0] < 0||F[1] < 0||N > Math.pow(10d, 18)) System.exit(1);

        if (N==0) {
            System.out.println(F[0]);
            System.exit(0);
        } else {
            F[2] = F[0] ^ F[1];
            F[0] = F[1];
            F[1] = F[2];
            F[2] = F[0] ^ F[1];
            System.out.println(F[((int) ((N - 1) % 3L))]);
        }
    }
}