input_a:
 xor ah,ah
 int 16h
 cmp al,48   ; '0'
 jb input_a
 cmp al,57   ; '9'
 ja input_a
 mov bl,al
 
input_b:
 xor ah,ah
 int 16h
 cmp al,48   ; '0'
 jb input_b
 cmp al,57   ; '9'
 ja input_b
 mov cl,al
 
input_op:
 xor ah,ah
 int 16h
 cmp al,43   ; '+'
 je op_add
 cmp al,45   ; '-'
 je op_sub
 jmp input_op
 
op_add:
 add bl,cl
 cmp bl,9
 ja op_error
 jmp op_ok
 
op_sub:
 cmp bl,cl
 jb op_error
 cmp bl,0
 je op_error
 sub bl,cl
 jmp op_ok
 
op_error:
 jmp end
 
op_ok:
 
end:
 

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