package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
)

func configure(scanner *bufio.Scanner) {
	scanner.Split(bufio.ScanWords)
	scanner.Buffer(make([]byte, 1000005), 1000005)
}
func getNextString(scanner *bufio.Scanner) string {
	scanned := scanner.Scan()
	if !scanned {
		panic("scan failed")
	}
	return scanner.Text()
}
func getNextInt(scanner *bufio.Scanner) int {
	i, _ := strconv.Atoi(getNextString(scanner))
	return i
}
func getNextInt64(scanner *bufio.Scanner) int64 {
	i, _ := strconv.ParseInt(getNextString(scanner), 10, 64)
	return i
}
func getNextFloat64(scanner *bufio.Scanner) float64 {
	i, _ := strconv.ParseFloat(getNextString(scanner), 64)
	return i
}
func main() {
	fp := os.Stdin
	wfp := os.Stdout
	extra := 0
	if os.Getenv("I") == "IronMan" {
		fp, _ = os.Open(os.Getenv("END_GAME"))
		extra = 100
	}
	scanner := bufio.NewScanner(fp)
	configure(scanner)
	writer := bufio.NewWriter(wfp)
	defer func() {
		r := recover()
		if r != nil {
			fmt.Fprintln(writer, r)
		}
		writer.Flush()
	}()
	solve(scanner, writer)
	for i := 0; i < extra; i++ {
		fmt.Fprintln(writer, "-----------------------------------")
		solve(scanner, writer)
	}
}
func solve(scanner *bufio.Scanner, writer *bufio.Writer) {
	ff := make([]int64, 2)
	for i := 0; i < 2; i++ {
		ff[i] = getNextInt64(scanner)
	}
	n := getNextInt64(scanner)
	v := makeGrid(2, 2)
	for i := 0; i < 2; i++ {
		for j := 0; j < 2; j++ {
			v[i][j] = 1
		}
	}
	v[0][0] = 0
	for n > 0 {
		if n&1 == 1 {
			ff = mul(ff, v)
		}
		v = mulv(v)
		n >>= 1
	}
	fmt.Fprintln(writer, ff[0])
}
func mul(ff []int64, v [][]int64) []int64 {
	f := make([]int64, 2)
	for i := 0; i < 2; i++ {
		for j := 0; j < 2; j++ {
			f[i] = f[i] ^ (ff[j] * v[i][j])
		}
	}
	return f
}
func mulv(v [][]int64) [][]int64 {
	vv := makeGrid(2, 2)
	for i := 0; i < 2; i++ {
		for j := 0; j < 2; j++ {
			for k := 0; k < 2; k++ {
				vv[i][j] = vv[i][j] ^ (v[i][k] * v[k][j])
			}
		}
	}
	return vv
}
func makeGrid(h, w int) [][]int64 {
	index := make([][]int64, h, h)
	data := make([]int64, h*w, h*w)
	for i := 0; i < h; i++ {
		index[i] = data[i*w : (i+1)*w]
	}
	return index
}