Let N be the number that consists of 61 consecutive 3's.

Let M be the number that consists of 62 consecutive 6's.
What is the digit sum of N×M?

Details and assumptions
The digit sum of a number is the sum of all its digits. E.g. the digit sum of N is 3+3+3+…+3+3+3=3×61=183

Answer not 555.