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5. 51073 - Campus Tours for High Schools

APGC-1

Start: Feb.04.2017 at 06:00:00 PM
Finish: Feb.05.2017 at 02:00:00 PM
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Time limit 2000/4000/4000/4000 ms. Memory limit 65000/65000/65000/65000 Kb.
Question by Arbli Troshani.

Campus Tours for High Schools

Epoka University is organizing Campus Tours for high schools of Tirana this Tuesday. Each high school though, can come within a certain time period [ai, bi] only.

Question: You want to find the minimum number of bus trips so that all high schools are satisfied and within their planned timeframe.

Input specification The first line of the input contains the number of schools (n). Each of the following n lines contains two integers ai and bi (separated by a space) defining available time frame of the i-th high school (the school will be happy if the bus takes students within this time frame) where n is between 1 and 40,000 and 0 ≤ ai ≤ bi ≤ 23.

Output specification First print the minimum number m of time points on the first line and the integer values of m time points (separated by spaces) on the second line.

 Sample Input I
3
1 3
2 5
3 6
Sample Input II
4
4 7
1 3
2 5
5 6
Sample Output I
1
3
Sample Output II
2
3 6

Explanation: (for Sample 1:) There are three schools coming. And all schools are available at three o'clock. One bus is sufficient to take students from all three schools.

 
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