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To find the entrance, from the first numbered room, go in any direction. Thenceforth, subtract the number of the previous room from the current one. Use the first digit of the difference to select one of the following strings: 1 gives NSEWUD, 2 gives NWESDU, 3 gives USDNEW, 4 gives SUNDEW, 5 gives ENUDSW, 6 gives DWEUNS. Use the second digit to select a letter from the string, and go in that direction. Thus, room 64 to 105 gives a difference of 41. Take the first letter from the fourth string, and go South.