1. By replacing every $*$ in the expression $1 * 2 * 3 * 4 * 5 * \cdots * 2019 * 2020$ with a plus or minus sign ( + or - ), a long arithmetic expression is formed. Place the plus and minus signs in such a way that the result is the smallest possible positive number (greater than 0).

What is this result?
B1. 2 We look at the expression from back to front. By taking $2017-2018-2019+2020$, we get exactly zero. Before that, we choose $2013-2014-2015+2016$ and so on until $5-6-7+8$. At the beginning, we take $1+2+3-4$ and thus we get a result of 2.

Now we only need to show that the result is never equal to 1, making 2 the smallest possible positive result. This is easily seen by noting that the result is always even. The result 2 is even, and if we change a + to a - or vice versa, it does not change whether the result is even or not. All possible results are therefore even.