Coding Spree
View as PDFIt's almost report card time, so of course everyone has started
programming like mad. There are only  
 hours
left before the Sunday midnight deadline!
Luckily, you've earned your points gradually, so now you can just sit back and watch your classmates struggle. One of your friends in particular is really screwed, so he's decided to skip school all week and go on a coding spree.
Though your friend is lazy, he has done some problems on the Judge, so
now he has exactly  
 problems available to him.
No more problems will be posted until after the deadline, and he can't
get partial marks on any of these problems. Problem 
 is worth 
points and he knows in advance that he can solve it in 
 hours
.
You're not a very pleasant person, so you want to torture your friend a bit. You plan to calculate the most points your friend could possibly get by the deadline, just so you can taunt him with that number.
Input Specification
Line : The integers 
 and 
.
The next  lines: Line 
 contains the integers 
 and 
.
Output Specification
Output the maximum amount of points your friend can get in at most 
hours of coding.
Sample Input
8 48
10 7
5 1
50 30
5 1
10 5
100 1000
25 10
60 40
Sample Output
95
Explanation
Your friend only has  hours, and 
 problems to choose from. To
maximize his points, he should do problems 
, 
, 
, 
, and 
,
giving him 
 points in 
 hours.
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