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1925. British Scientists Save the World

Time limit: 1.0 second
Memory limit: 64 MB
The world is in danger! Aliens threw a mysterious device to Earth n years ago. Every year an unknown sign appeared on its screen and it started to make threatening sounds until someone entered something on its keyboard. It lasted till now. But recently British scientists have found out that this device is a bomb which is capable to destroy our world in split second. The signs, which the device displays on its screen, are numbers and for input the device expects numbers as well.
The aliens invented a smart protection: every year, in order to avoid an explosion, you had to enter a number, which is less than the number shown on the screen by two. Fortunately, aliens decided that it takes a lot of computing resources to check whether the input number is correct every year. That is why the test is carried out once in n + 1 years. Moreover, they check only that the sum of all numbers entered since the last test matches the expected one.
The good news is that all symbols, which the bomb showed, and all numbers, which were entered, were recorded and the scientists already finished decrypting. Recently a number k appeared on mysterious device's screen and the scientists are sure that this time can be a fatal one. So, you have a chance to save the world by finding out what number should be entered in order to avoid an explosion.


The first line contains two positive integers n, k. In the next n lines there are pairs of numbers bi, gi (bi is the number shown on device's screen, gi is the number entered in the i-th year). All the integers in the input data do not exceed 100.


Output one nonnegative integer to save the world from the explosion. If there is no such number output “Big Bang!”.


6 5
3 1
3 1
5 3
6 5
5 5
7 2
1 3
4 6
Big Bang!
Problem Author: Pavel Ageev
Problem Source: Ural Regional School Programming Contest 2012