13.374 Three candles have the same length but different thicknesses. The first candle was lit 1 hour earlier than the other two, which were lit simultaneously. At some point, the first and third candles had the same length, and 2 hours after this, the first and second candles had the same length. How many hours does it take for the first candle to burn out if the second candle burns out in 12 hours and the third in 8 hours?