Instructions: Given a math word problem, answer the following question. You might need to apply addition or subtraction mathematical operators on the numbers embedded in the text to answer the question and then only report the final numerical answer.
Input: charlie an aspiring inventor is planning to make some wings to fulfill his dream to fly around the world . he started by collecting feathers . he needs 900 feathers and he already has 387 how many more feathers does he need to collect ?
Output:
513