You go to doctor and he injects you with 13 milligrams of radioactive dye. After twelve minutes, 4.75 milligrams of dye stay in your system. To leave doctor's office, you should pass through the radiation detector without sounding alarm. If detector will sound alarm whenever more than 2 milligrams of dye are in the system, how long will visit to doctor take, if you were given dye as soon as you arrived and amount of dye decays exponentially?