Since one month i left smoking. than i have very bad smell in my mouth please tell the medicine?

There is no medicine: Bad breath, or halitosis, can be caused by many things, and after only one month, many of the effects of your cigarette smoking may still be present. Gum disease, caused by inadequate flossing, is one of the more common causes, but there are many causes. See your dentist or physician for a good oral examination. Proper brushing (consider an electric one) flossing and mouthwashes may all help.

Renewed sensations: Smoking kills off some of your ability to smell and this begins to return, sometimes dramatically a week after you quit smoking. The smell, and or taste is likely what has been ongoing for some time, and you need to consult with your dentist about how to deal with it.