7. There are 100 chess pieces, and two people take turns to take the pieces. Each time, you are allowed to take 1 or 2 pieces. The one who takes the last piece wins. If you go first, how many pieces should you take the first time to ensure a win?
【Analysis】 $100 \div(1)+2=33 \cdots 1$, first take 1, making the number of stones 99, then adopt the following strategy: if the opponent takes 2, then take 1; if the opponent takes 1, then take 2. This way, the number of stones can always be a multiple of 3. Thus, the second player always faces a multiple of 3, and can only change it to a number that is not a multiple of 3, so the second player cannot make the number of stones 0, the first player wins.