The task is to generate the correct answer for a given math problem.

Example Input: Problem: in a group of 150 readers who read science fiction or literacy works or both , 120 read science fiction and 90 read literacy works . how many read both science fiction and literacy works ?
Example Output: 60

Example Input: Problem: a cycle is bought for rs . 900 and sold for rs . 1080 , find the gain percent ?
Example Output: 20 %

Example Input: Problem: how many diagonals does a polygon with 13 sides have , if one of its vertices does not connect to any diagonal ?
Example Output:
54