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

public class Solution {

    public static void main(String[] args) {
        
        Scanner scan = new Scanner(System.in);
        
        int a = scan.nextInt();
        int b = scan.nextInt();
        int t = scan.nextInt();
        long modded = 1000000007;
        long result = (int) (((0.5 * a * t) + (0.5 * b * t)) % modded);
        System.out.println(result);
    }
}