Because "two people take turns to count off, which must be a natural number of 1-5", the largest number in a round is "10" and the smallest number is "2". If the first player (replaced by A below) wants to win, he must count off after the penultimate round, and the total is 294, so that no matter what the opponent reports "10".

But because 294/6=49, there is no remainder, so the person who gives the number first in this question can't guarantee victory.