limit field to max 100 percent of 0 to 100 value

Dear Sir,

I am looking for Java script, i want a script where the field automatically deduct that the percentage going higher than number 100 and can place the decimal after 2 digits automatically, this way i can enforce a customer to write the right percentage from o to 100, actually when we allow field to type 5 digits a person can write 12345, now i want the field to know to place decimal after 2 diigits, so if the person is writing 99999 the figure should turn into 99.999. but using default decimal setting in Acrobat its not possible cause decimal adds after you right the  figure and enter like 99999.000

regards