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

public class Solution {

    public static void main(String[] args) {
        /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */
        Scanner scan=new Scanner(System.in);
        int a=scan.nextInt();
        int b=scan.nextInt();
        long n=scan.nextLong();
        int t=7;
        int ans=(int)((a*n*0.5)%t+(b*n*0.5)%t)%t;
        System.out.print(ans);
    }
}