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) {
        
        //Read in input
        Scanner scanner = new Scanner(System.in);
        
        //BigDecimal and BigInteger are unbounded numbers (limited only by RAM)
        BigDecimal a = scanner.nextBigDecimal();
        BigDecimal b = scanner.nextBigDecimal();
        BigDecimal t = scanner.nextBigDecimal();
        BigDecimal p_a = BigDecimal.valueOf(0.5);
        BigDecimal p_b = BigDecimal.valueOf(0.5);
        
        
        //Calculate final growth and convert to integer
        //Breaking down this formula: (p_a * a * t + p_b * b * t) % (Math.pow(10, 9) + 7)
        
        //p_a * a * t
        BigDecimal temp = p_a.multiply(a);
        temp = temp.multiply(t);
        
        //p_b * b * t
        BigDecimal temp2 = p_b.multiply(b);
        temp2 = temp2.multiply(t);
        
        //Compute first and second term
        
        //(p_a * a * t + p_b * b * t)
        BigDecimal firstTerm = temp.add(temp2);
        
        //Math.pow(10, 9) + 7
        BigDecimal secondTerm = BigDecimal.valueOf(Math.pow(10,9)+7);
               
        //Result is given by (First Term) % (Second Term)
        BigDecimal result = firstTerm.remainder(secondTerm);
        
        //Convert to BigInteger
        BigInteger finalGrowth = result.toBigInteger();
        
        //Print result
        System.out.println(finalGrowth);
        
    }//end main
}//end Solution