Assembly language, MASM.

I am to calculate the Nth number in the fibonacci sequence. Here is what I have so far and it is giving me garbage values...Please help me fix it!!

.586

.MODEL FLAT

INCLUDE io.h ; header file for input/output

.STACK 4096

.DATA ; declarations

mov eax, 1 ;a

mov ebx, 1 ;b

n WORD ?

prompt1 BYTE "Enter number to calculate to:", 0

string BYTE 40 DUP (?)

resultLbl BYTE "The sequence is", 0

sum BYTE 11 DUP (?), 0

.CODE

_MainProc PROC

input prompt1, string, 40 ; read ASCII characters

atod string ; convert to integer

mov ax, n ; store in memory

mov cx,0

_fib:

cmp cx,ax

jnl endFib

mov edx, eax ;move 1

add edx, ebx ;sum = a + b

mov eax, ebx ;a = b

mov ebx, edx ;b = sum

jmp _fib

endFib:

dtoa sum,ebx

output resultLbl, sum ; output label and sum

mov eax, 0 ; exit with return code 0

ret

_MainProc ENDP

END ; end of source code