One thief entered a cave where he found a pile of diamonds. At first he…

One thief entered a cave where he found a pile of diamonds. At first he thought of taking all of them, but listening to his conscience, he decided to take only half of them. While returning, he picked up two more diamonds from the pile. After that, a second thief entered the cave, took half of the remaining diamonds, and also picked up two more while returning. A third thief entered and did the same, and so did a fourth thief. When the fifth thief entered, he found only one diamond left in the cave. How many diamonds were there in the cave at first?