Calculating matrix inverse

Use any method you like to find the inverse of the next upper triangular matrix:

$$A = \begin{bmatrix} 1 & 2 & 3 \\ 0 & 1 & 4 \\ 0 & 0 & 1 \end{bmatrix}$$

Which method was faster? Enter the inverse in the following format:

0 0 0
0 0 0
0 0 0