import java.util.Scanner;

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