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) {
        Scanner input = new Scanner(System.in);
        int [] inp = new int[3];
        double output = 0;
        for (int i = 0;i<3;i++)
           inp[i]= input.nextInt();
        output = ((inp[0]+inp[1])*0.5*inp[2])%(Math.pow(10,9)+7);
        System.out.println((int)output);
        
    }
}