1.0 times take 2 pieces.

2. 1 time ........

3.2 times ........

.....

. N/2 times ......

All the situations add up.

Then multiply it by 2 (if you don't multiply it by 2, one person will catch it first)

When n=3n+ 1 or 3n+2, the person who catches first will definitely win.

(n= 1，2，3，......)

Explanation:

You can win directly when you have 1 or 2 pieces left.

So in the end, you must leave each other three coins.

In this way, no matter how many pieces the opponent takes, there will be 1 or 2 pieces left in the end.

You can win.

If you want to leave three coins for your opponent, you need to have four or five coins in the coin pile when you take them, so as to control the opponent's coins to three.

If you need to have 4 or 5 coins in the stack when you pick up coins, let your opponent have 6 coins in the stack when you pick up coins.

.......

When the opponent always takes it, the number of coins in the coin pile is always a multiple of 3.

In this way, the person who takes it first wins.