import java.util.Scanner;

public class Main {
	
	public static void main(String[] args){
		Scanner s = new Scanner(System.in);
		
		String[] str = s.nextLine().split(" ");
		s.close();
		
		double b1 = Double.parseDouble(str[0]);
		
		double b2 = Double.parseDouble(str[1]);
		
		double b3 = Double.parseDouble(str[2]);
		

		double b4 = Math.round((b3 - b2) / (b2 - b1) * b3 + (b2*b2-b1*b3)/(b2-b1));
		System.out.println((long)b4);
		
	}

}