There is a bridge with a sentry tower that connects two contries. A guard in the sentry tower comes out to check on the bridge every 2 minutes. Anyone trying to get into country A from over the bridge will be ordered back to country B, and anyone trying to leave country A without a pass will be shot.
Someone without a pass needs to get across the bridge, leaving country A and entering country B, but it will take them almost 4 minutes to cross the bridge. How might they get across?
(There is no sort of cover on the bridge that would allow them to stay out of sight, and no other way to cross than using the bridge).