Neko is crazy at solving the algorithm problems recently. He sets a plan for himself:
The \(1^{st}\) day, he will get on 1 problem solved.
The \(2^{nd}\) day, he will get on 3 problems solved.
The \(3^{rd}\) day, he will get on 6 problems solved.
...
The \(n^{th}\) day, he will get on \(n(n+1)/2\) problems solved.
Neko wants to know how many problems he will solve after \(K\) days.