Following texts are corrected description.

The USA Computer Security Office claims that the terrorist attack on 11th of September could not be scheduled without the help of scheduler programs that minimize the period of hijacking 4 planes and tower crashing. To check this claim, Information Ministry decided to write such a program and check if the result of the program is the same as the hijacking plan on September 11th. Terrorist's plan is to hijack some planes, immediately after take off and redirect them in order to hit the target towers. Each hijacked plane can be used for hitting at most one tower. The program input is the scheduling of the flights, and the position of main US towers. It's supposed that terrorists want to damage at least d towers and they want to minimize the period between the first and the last tower crash.