3090：Go Home

There comes the holiday, Partychen set foot on the way home. He takes some ECNU coins to hire bodyguards to prevent from being robbed before he went home. But the bodyguard takes one coin for every kilometer. If Partychen walks without bodyguard , he will be robbed one ECNU coin by every robber on every kilometer . Of course , he can choose where to hire bodyguard or where to be robbed as he like.
For example , there are two roads on his way home and he wants to use 8 ECNU coins to hire bodyguard , the first road takes 4 kilometers with 5 robbers ( per kilometer ) and the second takes 5 kilometers with 6 robbers. He could choose the last 3 kilometers on the first road and the whole kilometers on the second road to hire bodyguard to protect him, and leave the first kilometer on the first road to be robbed by 5 robbers, which he will be robbed 5 ECNU coins.
Now , Partychen want to know how many ECNU coins will be robbed at least.

It consists of multi-case .
Every case starts with two integers N and M ( 0≦N≦10,000, 0≦M≦1,000,000,000 ) which means that there are N roads and M ECNU coins to hire bodyguard.
The followed N lines contains two integers D and P (1<=D<=10,000 , 0<=P<=10 ) , which means the length of every road and the number of robbers in every kilometer on this road.
End with N=0 and M=0 .

An integer means the number of ECNU coins to be robbed at least.