Giải bài trực tuyến

"Phú ông" has a card deck consits of n cards. He writes on each card a number from 1 to n from the top to the bottom of the deck.
Then he does shuffle the card deck several times, each time is described by S(i, j) meaning: pull out the i^th card then put it on the j^th of the remaining cards (1 ≤ i, j ≤ n). If j = n, the i^th card will be the bottom card of the new one.
For example (n=6):

Afer x times of shuffing, "Phú ông" gives "Bờm" the card deck and chanllenges him to make it into the original order. Please help "Bờm"!

Input

- The first line contains two integer n, x.
- Next x line(s), the p^th line contains two integer i_p, j_p describing the p^th time of shuffing (S(i_p, j_p)).

Output

- A single integer means the minimal number of times of shuffing the card deck to help "Bờm".

Example

Input:
6 4
2 3
1 2
4 5
1 6

Output:
2

Limitations

- 1 ≤ n, x ≤ 10⁵.