(define (comb m n)
(define (citer mm nn prod)
(if (> mm m) prod
(citer (+ mm 1) (- nn 1) (/ (* prod nn) mm))))
(citer 1 n 1))
(define (solve nn)
(define (addto m n)
(if (> m n) 0
(+ (comb m n) (addto (+ m 2) (- n 2)))))
(+ 1 (addto 2 (- nn 1))))
(display (solve 50))
(newline)