Union of segments
Solving the problem from the quiz in mathematics, Vasya received the answer in the form of union of n segments [l[i], r[i]] on the number line. However, some of these segments may intersect with each other, that Vasya does not like too much.
Your task is to present Vasya's answer as a union of the minimum number of segments.
Input
The first line contains number n (1 ≤ n ≤ 50000). The following n lines contain pairs of integers l[i] and r[i] (|l[i]|, |r[i]| ≤ 50000), each pair is on a new line, numbers in pairs are separated from each other by one or more spaces.
Output
On the first line print number m - the number of segments in the desired union. In the next m lines print these segments in the same format as in the input. The list of segments must be sorted in ascending order of the left end.