(define abs
    (lambda (n)
        (if (< n 0)
            (- 0 n)
            n)))
(define frac (lambda (n) (- n (int n))))
(define truncate int)
(define floor
    (lambda (n)
        (int
            (if (< n 0)
                (- n 1)
                n))))
(define ceiling (lambda (n) (- 0 (floor (- 0 n)))))
(define round (lambda (n) (floor (+ n 0.5))))
(define mod (lambda (n m) (- n (* m (int (/ n m))))))
(define gcd
    (lambda (n m)
        (if (eq? m 0)
            n
            (gcd m (mod n m)))))
(define lcm (lambda (n m) (/ (* n m) (gcd n m))))
(define even? (lambda (n) (eq? (mod n 2) 0)))
(define odd? (lambda (n) (eq? (mod n 2) 1)))