import java.util.Scanner;

class Yuki64 {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    long a = sc.nextLong();
    long b = sc.nextLong();
    long n = sc.nextLong();
    long x = 0;
    if(n>=2){
      x = fib(b,a,n);
    } else if(n==0){
      x = a;
    } else if(n==1){
      x = b;
    }
    System.out.println(x);
  }

  private static long fib(long b,long a,long n) {
    long c = b^a;
    n-=1;
    if(n==1) return c;
    return fib(c,b,n);
  }
}