import java.io.*;
import java.util.*;
import java.math.*;

class Main64 {
	
	public static void out (Object out) {
		System.out.println(out);
	}
	
	public static void main (String[] args) throws IOException {
		BufferedReader br = 
			new BufferedReader(new InputStreamReader(System.in));
		
		String[] line = br.readLine().split(" ");
		long f0 = Long.parseLong(line[0]);
		long f1 = Long.parseLong(line[1]);
		long n  = Long.parseLong(line[2]);
		
		out(n % 3 == 0 ? f0 : n % 3 == 1 ? f1 : f0^f1);
		
	}
}