package main

import "fmt"

func main() {
    var a, b, n int64
    fmt.Scan(&a, &b, &n)
    xorFib := make([]int64, n+1)
    xorFib[0] = a
    xorFib[1] = b

    for i := int64(2); i <= n; i++ {
        xorFib[i] = xorFib[i-2] ^ xorFib[i-1]
    }

    fmt.Println(xorFib[n])
}