Trick or Treat

Halloween was almost over, and Mr.Green had less than 20 candies left. When the doorbell rang, he thought he would give all the candies away. When he opened the door, there were 2 trick or treaters. He wanted to give away the candies evenly, but he noticed that when he divided the candies in 2, there was 1 left over. At that point, he saw another trick or treater behind the first 2. He tried to divide the candies evenly among the 3 of them, but again 1 was left over. Finally, another trick or treater came to his door, making it 4 trick or treaters altogether. Mr. Green have still had 1 candy left over after dividing the left over candies in fours. How many candies did Mr. Green have left when the doorbell rang?