.model small
.stack 100h
.data
buffer db 20       ; Max length
       db 0        ; Actual length (filled in by DOS)
       db 20 dup(?) ; The actual input string

.code
mov ax, @data
mov ds, ax

mov ah, 0Ah        ; DOS function: buffered input
lea dx, buffer     ; Load address of buffer
int 21h            ; Call DOS to get the string

; Now, buffer+2 points to the start of the actual string
; buffer+1 tells you how many characters were read

mov ah, 4Ch        ; Exit program
int 21h
end