package test;

import java.util.Scanner;

public class Main {
    public static void main(String[] args){
       Scanner in = new Scanner(System.in);
       int b1 = in.nextInt();
       int b2 = in.nextInt();
       int b3 = in.nextInt();

       double r = (b3 - b2) / ((b2 - b1) * 1.0);
       double d = b3 - r * b2;
       System.out.println((int)(r * b3 + d));
    }
}