Merge Intervals

Given an array of intervals where intervals[i] = [start, end], merge all overlapping intervals and return non-overlapping intervals. Algorithm: Sort by start time, then iterate and merge if current start ≤ previous end. Example: [[1,3],[2,6],[8,10],[15,18]] → [[1,6],[8,10],[15,18]] (intervals [1,3] and [2,6] overlap)

Input

Line 1: n (number of intervals). Next n lines: start end (space-separated).

Output

Merged intervals, one per line as 'start end'.

Sample

4
1 3
2 6
8 10
15 18

Expected

1 6
8 10
15 18