A man who lived in Mexico wanted to cross the Mexico/America border. The bridge which he is to cross is a half mile across, over a large gap. Every three minutes a guard comes out of his bunker and checks if anyone is on the bridge. If a person is caught trying to escape Mexico side to the America side they are shot. If caught crossing the other direction without papers they are sent back. He knows that it takes at least five minutes to cross the bridge, in which time the guard will see him crossing and shoot him. How does he get across?