Iahub got lost in a very big desert. The desert can be represented as a *n* × *n* square matrix, where each cell is a zone of the desert. The cell (*i*, *j*) represents the cell at row *i* and column *j* (1 ≤ *i*, *j* ≤ *n*). Iahub can go from one cell (*i*, *j*) only down or right, that is to cells (*i* + 1, *j*) or (*i*, *j* + 1). 

Also, there are *m* cells that are occupied by volcanoes, which Iahub cannot enter. 

Iahub is initially at cell (1, 1) and he needs to travel to cell (*n*, *n*). Knowing that Iahub needs 1 second to travel from one cell to another, find the minimum time in which he can arrive in cell (*n*, *n*).
The first line contains two integers *n* (1 ≤ *n* ≤ 10<sup class="upper-index">9</sup>) and *m* (1 ≤ *m* ≤ 10<sup class="upper-index">5</sup>). Each of the next *m* lines contains a pair of integers, *x* and *y* (1 ≤ *x*, *y* ≤ *n*), representing the coordinates of the volcanoes.

Consider matrix rows are numbered from 1 to *n* from top to bottom, and matrix columns are numbered from 1 to *n* from left to right. There is no volcano in cell (1, 1). No two volcanoes occupy the same location.
print("_RANDOM_GUESS_1689644519.174965")# 1689644519.1749845