I need help coding this lc3 assembly program. Basically I need to make a calculator using LC3 assembly language and perform + - * and / operations. It works fine but.... ***I want to edit it so that it can also do addition and so it can accept up to 4 integers as input numbers. Currently, it accepts single digit input numbers*** The code:

.ORIG x3000
	START:
	; clear registers that are used
	AND R0, R0, 0
	AND R1, R0, 0
	AND R2, R0, 0
	; print greetings and get input
	LEA R0, GREETING
	PUTS
	GETC
	PUTC
	ADD R1, R0, 0
	LEA R0, FOLLOWUP
	PUTS
	GETC
	PUTC
	ADD R2, R0, 0
	; subtract the ASCII offset from the numbers to convert them from their ASCII values
	LD R0, ASCIIOFFSET
	ADD R1, R1, R0
	ADD R2, R2, R0
	; perform operations and store answers in the designated memory locations
	JSR SUBTRACT
	JSR MULTIPLY
	JSR DIVIDE
	; convert back to ASCII
	LD R0, ASCIIOFFSET
	NOT R0, R0
	ADD R0, R0, #1
	ADD R1, R1, R0
	ADD R2, R2, R0
	; print results
	ST R1, INPUT1
	ST R2, INPUT2
	LEA R0, NEWLINE
	PUTS
	LD R0, INPUT1
	PUTC
	LEA R0, MINUS
	PUTS
	LD R0, INPUT2
	PUTC
	LEA R0, EQUALS
	PUTS
	LDI R0, SUBRESULT2
	PUTC
	LEA R0, NEWLINE
	PUTS
	LD R0, INPUT1
	PUTC
	LEA R0, TIMES
	PUTS
	LD R0, INPUT2
	PUTC
	LEA R0, EQUALS
	PUTS
	JSR PRINTMULT ; subroutine to print bigger values properly
	LEA R0, NEWLINE
	PUTS
	LD R0, INPUT1
	PUTC
	LEA R0, DIVIDEDBY
	PUTS
	LD R0, INPUT2
	PUTC
	LEA R0, EQUALS
	PUTS
	LDI R0, DIVRESULT2
	PUTC
	LEA R0, REMAINDING
	PUTS
	LDI R0, REMAINDER2
	PUTC
	; store values into x3100-3103 as required, after dealing with the subroutine that uses those lines
	LD R0, SUBRESULT2
	ST R0, SUBRESULT
	LD R0, MULRESULT2
	ST R0, MULRESULT
	LD R0, DIVRESULT2
	ST R0, DIVRESULT
	LD R0, REMAINDER2
	ST R0, REMAINDER
	; finish off with a newline and loop
	LEA R0, NEWLINE
	PUTS
	BR START
	HALT
	; strings
	GREETING: .STRINGZ "This program will perform operations on your input. Please enter a single-digit number: "
	FOLLOWUP: .STRINGZ " Now enter another one: "
	NEWLINE: .STRINGZ " "
	MINUS: .STRINGZ " - "
	TIMES: .STRINGZ " * "
	DIVIDEDBY: .STRINGZ " / "
	REMAINDING: .STRINGZ " R"
	EQUALS: .STRINGZ " = "
	; variables
	ASCIIOFFSET: .FILL #-48
	SUBRESULT: .FILL x3100
	MULRESULT: .FILL x3101
	DIVRESULT: .FILL x3102
	REMAINDER: .FILL x3103
	INPUT1: .FILL 0
	INPUT2: .FILL 0
	TEMP: .FILL 0
	; for the weird line overwriting
	SUBRESULT2: .FILL x3140
	MULRESULT2: .FILL x3141
	DIVRESULT2: .FILL x3142
	REMAINDER2: .FILL x3143
	; functions/subroutines
	SUBTRACT:
	; clear used registers again
	AND R0, R0, 0
	AND R3, R0, 0
	NOT R4, R2 ; flip digit 2's (R2's) sign and store in R4
	ADD R4, R4, #1
	; subtract R1 by R4=R2 and store in R3
	ADD R3, R1, R4
	; convert back to ASCII
	LD R0, ASCIIOFFSET
	NOT R0, R0
	ADD R0, R0, #1
	ADD R3, R3, R0
	STI R3, SUBRESULT2 ; store answer
	RET
	MULTIPLY:
	; clear used registers again
	AND R0, R0, 0
	AND R3, R0, 0
	AND R4, R0, 0
	ADD R4, R2, 0 ; store loop incrementer (R2) in R4
	; multiply R1 by R2 and store in R3
	LOOP1:
	ADD R3, R3, R1 ; add R1 to R3 R4=R2 times
	ADD R4, R4, #-1
	BRp LOOP1 ; break if R4 is <=0
	STI R3, MULRESULT2 ; store answer
	RET
	DIVIDE:
	; clear used registers again
	AND R0, R0, 0
	AND R3, R0, 0
	AND R5, R0, 0
	AND R6, R0, 0
	ADD R5, R1, 0 ; store R1 in R5 so we can mess with R1's value
	NOT R4, R2 ; flip R2's sign again and store in R4
	ADD R4, R4, #1
	; divide R1 by R2 and store dividend in R3
	LOOP2:
	ADD R3, R3, #1 ; keep track of how many times it divides
	ADD R5, R5, R4 ; keep subtracting by divisor
	AND R6, R0, 0 ; use R6 as a buffer so that we break when R4>R5
	ADD R6, R5, 0
	ADD R6, R6, R4
	BRzp LOOP2 ; break if R6 is <0
	; convert back to ASCII
	LD R0, ASCIIOFFSET
	NOT R0, R0
	ADD R0, R0, #1
	ADD R3, R3, R0
	ADD R5, R5, R0
	STI R3, DIVRESULT2 ; store answer
	STI R5, REMAINDER2 ; store remainder
	RET
	PRINTMULT:
	; the compiler was putting the lines in this subroutine on x3100-3103, and so they were overwritten
	; I had to store the results in a different location and then put them back at the end
	; clear used registers again
	AND R3, R0, 0
	AND R4, R0, 0
	AND R5, R0, 0
	ADD R5, R7, 0 ; store RET value before using traps
	; get result into R0
	LDI R0, MULRESULT2
	; test for a small enough number to just print one digit
	ADD R3, R0, 0 ; store quotient in R3 in case we branch
	ADD R4, R0, #-10
	BRn ONEDIGIT
	; clear used registers again
	AND R3, R0, 0
	AND R4, R0, 0
	; divide by 10 and find remainder
	LOOP3:
	ADD R3, R3, #1 ; keep track of how many times it divides
	ADD R0, R0, #-10 ; keep subtracting by divisor
	AND R4, R0, 0 ; use R4 as a buffer so that we break when 10>R4
	ADD R4, R0, 0
	ADD R4, R4, #-10
	BRzp LOOP3 ; break if R4 is <0
	; test for a quotient of 0 and if so, just print remainder (which is R0)
	AND R4, R0, 0
	ADD R4, R3, #-1
	BRz DIVTEST
	DIVTESTFAIL:
	; print quotient and then load remainder to print
	AND R4, R0, 0
	ADD R4, R0, 0 ; store remainder to print quotient first
	; convert back to ASCII before printing
	LD R0, ASCIIOFFSET
	NOT R0, R0
	ADD R0, R0, #1
	ADD R3, R3, R0
	; store final value to print in a variable and load it into R0 so that PUTC is happy
	ST R3, TEMP
	LD R0, TEMP
	PUTC
	; put remainder in R3 to print
	AND R3, R0, 0
	ADD R3, R4, 0
	ONEDIGIT:
	; convert back to ASCII before printing
	LD R0, ASCIIOFFSET
	NOT R0, R0
	ADD R0, R0, #1
	ADD R3, R3, R0
	; store final value to print in a variable and load it into R0 so that PUTC is happy
	ST R3, TEMP
	LD R0, TEMP
	PUTC
	; restore RET value before going back
	AND R7, R0, 0
	ADD R7, R5, 0
	RET
	; test for a quotient of 0: if INPUT1 <= INPUT2, quotient is 0
	DIVTEST:
	LD R4, INPUT1
	NOT R4, R4
	ADD R4, R4, #1
	AND R6, R0, 0
	LD R6, INPUT2
	ADD R4, R4, R6
	BRn DIVTESTFAIL
	AND R3, R0, 0
	ADD R3, R0, 0
	BRzp ONEDIGIT
	; end of code
	.END

Thanks!