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 sc=new Scanner(System.in);
        int a=sc.nextInt();
        int b=sc.nextInt();
        int t=sc.nextInt();
        Double number;
        double result;
        number=(0.5*a*t)+(0.5*b*t);
        result=number%(Math.pow(10,9)+7);
        System.out.println((int)result);
        
    }
}