9. In a counter-terrorism game, a "terrorist" is hiding behind 10 windows arranged in a row, and a "counter-terrorist" with a perfect shot uses a sniper rifle to shoot the "terrorist". The "counter-terrorist" only needs to hit the window where the "terrorist" is hiding to hit him. After each shot, if the "terrorist" is not hit, he will move one window to the right. Once he reaches the rightmost window, he will stop moving. To ensure hitting the "terrorist", the "counter-terrorist" needs to shoot at least times. $\qquad$
【Answer】Solution:
First shot at window 1, the terrorist cannot appear at window 2; second shot at window 3, the terrorist cannot appear at window 4; third shot at window 5, the terrorist cannot appear at window 6; fourth shot at window 7, the terrorist cannot appear at window 8; fifth shot at window 9, the terrorist might be at window 10, so a sixth shot is needed.

According to the above analysis, at least 6 shots are required.