The Y Bus Goes Vroom

The bus that driver 비와이 drives leaves the first station, passes $N$ stops, and arrives at the last station. Each stop has a fixed number of people who get off and a fixed number who get on. At the last station everyone still on the bus gets off.

The first line has the number of stops between the first and the last station, $N$ ($1 \le N \le 100\,000$), and the number of people who board at the first station, $K$ ($1 \le K \le 10\,000$).

Each of the next $N$ lines has the number of people who board at the $i$-th stop, $A$, and the number of people who get off there, $B$ ($0 \le A, B \le 10\,000$).

Print the name of the bus driver at the moment the bus reaches the last station, on one line. Write the name in Hangul, exactly 비와이.