CF261C Maxim and Matrix

Maxim loves to fill in a matrix in a special manner. Here is a pseudocode of filling in a matrix of size $ (m+1)×(m+1) $ :  Maxim asks you to count, how many numbers $ m $ $ (1

A single line contains two integers $ n $ and $ t $ $ (1

In a single line print a single integer — the answer to the problem.