import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long b1 = sc.nextInt();
        long b2 = sc.nextInt();
        long b3 = sc.nextInt();
        long ans = ((b3 - b2) * (b3 - b2) + (b2 - b1) * b3) / (b2 - b1);
        System.out.println(ans);
    }
}