combinatorics - How to simplify this triple summation containing binomial coefficients?

$$\large\sum_{i=0}^{n} \sum_{j=i}^{n} \sum_{k=j}^{n} \binom{i+m-1}{m-1}\binom{j+m-1}{m-1}\binom{k+m-1}{m-1}$$

How to solve it when this involve more than thousand summation ?