import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.math.BigInteger;

public class Main {
	public static void main(String[] args) {
		BufferedReader buff = new BufferedReader(new InputStreamReader(System.in));

		try {
			String[] box = buff.readLine().split(" ");
			BigInteger[] f = new BigInteger[2];
			f[0] = new BigInteger(box[0]);
			f[1] = new BigInteger(box[1]);
			BigInteger n = new BigInteger(box[2]);

			if ((n.remainder(new BigInteger("3")).intValue()) < 2) {
				System.out.println(f[(n.remainder(new BigInteger("3")).intValue())]);
			} else {
				BigInteger w = f[0].xor(f[1]);
				System.out.println(w);
			}

		} catch (NumberFormatException e) {
			e.getStackTrace();
		} catch (IOException e) {
			e.getStackTrace();
		} catch (Exception e) {
			e.getStackTrace();
		}
	}
}