I succeed to solve it with a dynamic programming algorithm,
but the memory limits was very tough. To answer it I had to use
2 arrays: one for the first 300 rows of the array with a type of 4
bytes per number and one for the last 200 rows with a type of 8
bytes per number.

 Any details
 Can you tell me how to dp?
 3q

20 rows with a type of 8 bytes per number are enough.