#!/usr/bin/env -S guile -s
!#
(use-modules (ice-9 regex)
             (ice-9 textual-ports)
             (srfi srfi-1))

(define (read-lines port)
  (letrec ((loop (lambda (l ls)
                   (if (eof-object? l)
                       ls
                       (loop (get-line port) (cons l ls))))))
    (reverse (loop (get-line port) '()))))

(define (value-for-line line)
  (string->number (string-filter char-set:digit line)))

(define (travel-distance total-time hold-time)
  (* (- total-time hold-time) hold-time))

(let* ((port (open-input-file "6.txt"))
       (lines (read-lines port))
       (time (value-for-line (car lines)))
       (distance (value-for-line (cadr lines)))
       (current 0)
       (count 0))
  (close-port port)
  (while (<= current distance)
    (set! current (travel-distance time count))
    (set! count (1+ count)))
  (display (- (+ time 1) (* 2 (- count 1)))))