3.51 Merlin has two $100 \times 100$ grid tables, one is a blank table, hanging on the cliff at the cave entrance, and the other has a number in each cell, hanging on the wall inside the cave. You can specify any size square (it can be $1 \times 1, 2 \times 2, \cdots, 100 \times 100$) in the first table, and then pay one shilling to Merlin to find out the sum of the numbers in the corresponding sub-table in the second table. How many shillings do you need to pay at least to get the sum of the numbers on the diagonal of the second table?
［Solution］Obviously, by asking about 100 $1 \times 1$ squares along the diagonal, we can find out the sum of all numbers on the diagonal, so the minimum value we seek does not exceed 100.

On the other hand, if Merlin fills the second grid as shown in the figure below, then no matter which square is asked about, each question can reveal at most one number on the diagonal. Therefore, after asking 99 questions, it is still impossible to determine the sum of the numbers. Therefore, to find the sum of all numbers on the diagonal in the second grid, at least 100 shillings must be paid.