Tudor is buying ~N~ blocks of cheese. Each block of cheese has a regular price and a discounted price.
Tudor has ~K~ coupons that allow him to buy a block of cheese for the discounted price instead of the regular price. Each coupon can be used for exactly one block of cheese.
Given that Tudor wants to buy all ~N~ blocks of cheese, compute the minimum amount of money he must spend.
~1 \le N \le 10^5~
~0 \le K \le N~
~1 \le d_i \le p_i \le 10^9~
The first line contains two space separated integers, ~N~ and ~K~.
The next ~N~ lines each contain two space separated integers, ~p_i~ and ~d_i~ representing the regular price and discounted price of block ~i~, respectively.
Output the minimum amount of money Tudor must spend.
2 1 100 0 10 10