(define (sumt N K) 
	(begin
		(if (eq? K 1)
			(positivo N)
			(if (eq? K -1)
				(negativo N K)
			)
		)
	)
)
(define (negativo N K)
	(begin
		(if (> N 1)
			(begin
				(begin (define K1 (* K -1)))
				(+ (/ N (* (+ N 1) (+ N 2))) (* K1 (negativo (- N 1) K1)))
			)
			(if (eq? N 1)
				(/ 1 6)
			)
		)
	)
)
(define (positivo N)
	(begin
		(if (> N 1)
			(begin (+ (/ N (* (+ N 1) (+ N 2))) (positivo (- N 1))))
			(if (eq? N 1)
				(/ 1 6)
			)
		)
	)
)
(begin  (define N (read))
        (define K (read))
        (write (sumt N K))
)

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