import java.util.Scanner;
class N064{
	public static void main(String args[]){
		Scanner s = new Scanner(System.in);
		long f0 = s.nextLong();
		long f1 = s.nextLong();
		long n = s.nextLong();
		long f = 0;
		for(long i = 0; i < n -1; i++){
			f = f0 ^ f1;
			f0 = f1;
			f1 = f;
		}
		if(n == 0){
			System.out.println(f0);
		}else if(n == 1){
			System.out.println(f1);
		}else{
			System.out.println(f);
		}
	}
}