import java.io.*;
import java.util.*;

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();
        int t = in.nextInt();
        
        double expectedGrowthA = 0.5 * a * t;
        double expectedGrowthB = 0.5 * b * t;
        double totalExpectedGrowth = expectedGrowthA + expectedGrowthB;
        double result = totalExpectedGrowth % (Math.pow((double) 10, (double) 9) + 7);
        System.out.println((int) result);
        
    }
}