(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))
)
KGRlZmluZSAoc3VtdCBOIEspIAoJKGJlZ2luCgkJKGlmIChlcT8gSyAxKQoJCQkocG9zaXRpdm8gTikKCQkJKGlmIChlcT8gSyAtMSkKCQkJCShuZWdhdGl2byBOIEspCgkJCSkKCQkpCgkpCikKKGRlZmluZSAobmVnYXRpdm8gTiBLKQoJKGJlZ2luCgkJKGlmICg+IE4gMSkKCQkJKGJlZ2luCgkJCQkoYmVnaW4gKGRlZmluZSBLMSAoKiBLIC0xKSkpCgkJCQkoKyAoLyBOICgqICgrIE4gMSkgKCsgTiAyKSkpICgqIEsxIChuZWdhdGl2byAoLSBOIDEpIEsxKSkpCgkJCSkKCQkJKGlmIChlcT8gTiAxKQoJCQkJKC8gMSA2KQoJCQkpCgkJKQoJKQopCihkZWZpbmUgKHBvc2l0aXZvIE4pCgkoYmVnaW4KCQkoaWYgKD4gTiAxKQoJCQkoYmVnaW4gKCsgKC8gTiAoKiAoKyBOIDEpICgrIE4gMikpKSAocG9zaXRpdm8gKC0gTiAxKSkpKQoJCQkoaWYgKGVxPyBOIDEpCgkJCQkoLyAxIDYpCgkJCSkKCQkpCgkpCikKKGJlZ2luICAoZGVmaW5lIE4gKHJlYWQpKQogICAgICAgIChkZWZpbmUgSyAocmVhZCkpCiAgICAgICAgKHdyaXRlIChzdW10IE4gSykpCik=