Pascal's triangle

Print the first $n$ rows of Pascal's triangle. Every row starts and ends with $1$, and every number in the middle is the sum of the two neighbouring numbers in the row above:

1
1 1
1 2 1
1 3 3 1
1 4 6 4 1

A single integer $n$ ($1 \le n \le 30$).

$n$ lines: line $i$ contains $i$ numbers separated by spaces.

Keep the previous row and build the next one from it: element $j$ of the new row is the sum of elements $j - 1$ and $j$ of the previous row. The largest number is $77\,558\,760$ — it fits into an int.