18. (6 points) December 31, 2013, was a Tuesday, so, June 1, 2014, is $\qquad$. (Answer with a number: Monday is represented by 1, Tuesday by 2, Wednesday by 3, Thursday by 4, Friday by 5, Saturday by 6, and Sunday by 7.)
【Analysis】First, calculate the number of days from December 31 to June 1, then determine how many weeks and extra days are in this period, and finally judge based on the remainder.

【Solution】Solution: $2014 \div 4=503 \cdots 2$
So this year is a common year, February has 28 days,
$1, 3, 5$ are large months with 31 days, April is a small month with 30 days,
There are $28+31 \times 3+30+1=152$ (days)
$$
152 \div 7=21 \cdots 5
$$

The remainder is $5, 2+5=7$
Answer: Therefore, June 1, 2014, is a Sunday;
The answer is: 7.