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();
        long t = in.nextLong();
        
        double number = (0.5 * a * t) + (0.5 * b * t);
        double modulo = Math.pow(10, 9) + 7;
        int result = (int)(number % modulo);

        System.out.println(result);
    }
}