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 in = new Scanner(System.in);
        
        int a = in.nextInt();
        int b = in.nextInt();
        
        long mili = in.nextLong();
        
        double cells = (.5 * a * mili) + (.5 * b * mili);
        
        double mod = cells % (Math.pow(10, 9) + 7);
        
        long toPrint = Math.round(mod);
        
        System.out.println(toPrint);
        
    }
}