(define (solve a b i)
 (if (> i b) 0 
  (if (= (remainder (+ (+ a b ) i) 3) 0) (+ 1 (solve a b (+ i 1))) (solve a b (+ i 1))) 
  ) 
)
(let* ((a (read)) 
       (b (read))) 
       (print (solve a b a)))