15. Find the sum:

$$
1+2-3-4+5+6-7-8+\ldots+301+302
$$
15. Let's write the sum as follows: $1+(2-3-4+5)+(6-7-8+9)+\ldots+(298-$ $-299-300+301)+302$. In each parenthesis, we get 0, so the final result is $1+302=303$.