import java.util.Scanner;

public class No353 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long A = sc.nextLong();
		long B = sc.nextLong();
		
		if(A-B != 0) {
			System.out.println((A*A - B*B) / (A-B));
		}else if(A == 0 && B != 0) {
			System.out.println(B);
		}else if(A != 0 && B == 0) {
			System.out.println(A);
		}else if(A != 0 && B != 0 && A - B == 0) {
			System.out.println(A*2);
		}else {
			System.out.println(0);
		}
	}
}