Question

To override a presidential veto, at least

Answer 1

67 people need to vote

even though 2/3 is 66.66, it need to be rounded up to 67

Answer 2

To answer this question, you need to round to the nearest whole number, because you cannot have two thirds of a senator vote.  Since two thirds rounds up to 1, your answer would be 66 + 1, which is 67.  Therefore, the minimum number of votes to override a veto is 67 votes.