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) throws Exception
    {
        /* Enter your code here. Read input from STDIN. Print output to STDOUT. Your class should be named Solution. */
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String val[]= br.readLine().split(" ");
        
        final float half = 0.5f;
        final byte A = Byte.parseByte(val[0]);
        final byte  B = Byte.parseByte(val[1]);
        long dur = Long.parseLong(val[2]);
        
        double cal = 0;
        cal = (half * A *dur ) + (half * B * dur);
        
       dur  = (long) cal % (1000000000 + 7 );
        System.out.print(dur);
    }
}