In his twenties, Manager was a passionate racing driver. He got his first 105LS (Speed Laser) to his 18th birthday. For a while, thanks to her, she even seemed to be a career manager of a successful manager - and that will be the career of a successful driver. Although it was a standard old, rusty skidder, which itself took off excess parts, had a Manager-and respect because she was a peer. And of course - it was her - Barbara.
Loss of excess parts even happened on the dashboard when the wrecker dropped from the speedometer. Although the Manager, as the correct representative of the DIY movement, managed to stuck it back, it soon found out that he had stuck it at the wrong angle. So even if the tachometer showed the value of the current velocity v, its actual value was in + k, where k is an unknown constant (probably negative).
So the manager began to make honest notes of the rides he had gone through to find out the value of the mysterious constant to. Records from each drive consist of n parts. Each part of the drive contains the distance traveled s and the speed value v, which was then indicated by the speedometer. The whole record took time t. Help the Manager create a program to get the secret value of k from the measured data.
entry
The first line of input contains two integers: n (1 ≤ n ≤ 1000), which represents the number of parts of a single drive, and t (1 ≤ t ≤ 10 ^ 6), which represents the total driving time. This is followed by n lines, each of which describes one part of the drive that the Manager has recorded. Each row contains two integers: s (1 ≤ s ≤ 1000) and v (| v | ≤ 1000), the distance and speed indicated by the tachometer with the hand stuck during that part of the trip. The time is given in hours, the distance in kilometers and the speed in kilometers per hour.
Output
Mysterious constant k given in kilometers per hour. However, the deviation in your response must be less than 6 decimal places.
