Can someone help me with this problem, any help will be appreciated.

Problem Statement: Bob wants to purchase N pens and so has prepared a list of shops that sell the pens. Each shop charges a different price per pen and has a limited quantity available in stock. Along with the price of the pen, each shop charges fixed delivery fees irrespective of how many pens are bought. Write a program to help Bob get the N pens as cheaply as possible.

Input Format: The first input line has two integers: N, the number of pens Bob needs, and S, the number of shops. Next, S lines have 3 integers, Q, P, and D, where Q is the stock of pens available at the shop, P is the price per pen and D is the delivery fee.

Output Format: A single line of output has an integer, which is the minimum amount Bob has to spend to purchase N pens.

Constraints: 1) 1 <= N <=10000 11) 1 <= S <= 100 lI1) 0 <= 0 <= 10000 IV 0 <= P<= 10000 V) O<= D <= 1000000 VI) N<= 01+Q2+...+Qs