import java.util.*;
import java.util.Arrays;

public class Main {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		long a1 = sc.nextLong();
		long a2 = sc.nextLong();
		long a3 = sc.nextLong();
		System.out.println((a3*(a3-a1)+a2*(a2-a3))/(a2-a1));
	}
}