#lang racket

(define (solution)
  (define cs (for/list ((i (begin0 (read) (read-line))) (j (in-port read-char))) j))
  (let loop ((cs cs) (alt 0) (rv 0))
    (match* (cs alt)
      [((list) _) rv]
      [((cons #\U tl) (app add1 alt+)) (loop tl alt+ rv)]
      [((cons #\D tl) 0) (loop tl -1 (add1 rv))]
      [((cons #\D tl) (app sub1 alt-)) (loop tl alt- rv)])))

(solution)