Write a program that: finds the minimal number of elements in a set containing at least two different integers from each interval.

The first line of the input contains the number of intervals n, 1 <= n <= 10000. Each of the following n lines contains two integers a, b separated by a single space, 0 <= a < b <= 10000. They are the beginning and the end of an interval.

Process to the end of file.

Output the minimal number of elements in a set containing at least two different integers from each interval.

4 3 6 2 4 0 2 4 7

4

CEOI 1997