Score : 300 points
We have N ID cards, and there are M gates.
We can pass the i-th gate if we have one of the following ID cards: the L_i-th, (L_i+1)-th, ..., and R_i-th ID cards.
How many of the ID cards allow us to pass all the gates alone?
Input is given from Standard Input in the following format:
N M L_1 R_1 L_2 R_2 \vdots L_M R_M
Print the number of ID cards that allow us to pass all the gates alone.
4 2 1 3 2 4
2
Two ID cards allow us to pass all the gates alone, as follows:
10 3 3 6 5 7 6 9
1
100000 1 1 100000
100000