CF1495B.Let's Go Hiking

普及/提高-

通过率:0%

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题目描述

On a weekend, Qingshan suggests that she and her friend Daniel go hiking. Unfortunately, they are busy high school students, so they can only go hiking on scratch paper.

A permutation pp is written from left to right on the paper. First Qingshan chooses an integer index xx ( 1xn1\le x\le n ) and tells it to Daniel. After that, Daniel chooses another integer index yy ( 1yn1\le y\le n , yxy \ne x ).

The game progresses turn by turn and as usual, Qingshan moves first. The rules follow:

  • If it is Qingshan's turn, Qingshan must change xx to such an index xx' that 1xn1\le x'\le n , xx=1|x'-x|=1 , xyx'\ne y , and px<pxp_{x'}<p_x at the same time.
  • If it is Daniel's turn, Daniel must change yy to such an index yy' that 1yn1\le y'\le n , yy=1|y'-y|=1 , yxy'\ne x , and py>pyp_{y'}>p_y at the same time.

The person who can't make her or his move loses, and the other wins. You, as Qingshan's fan, are asked to calculate the number of possible xx to make Qingshan win in the case both players play optimally.

输入格式

The first line contains a single integer nn ( 2n1052\le n\le 10^5 ) — the length of the permutation.

The second line contains nn distinct integers p1,p2,,pnp_1,p_2,\dots,p_n ( 1pin1\le p_i\le n ) — the permutation.

输出格式

Print the number of possible values of xx that Qingshan can choose to make her win.

输入输出样例

  • 输入#1

    5
    1 2 5 4 3

    输出#1

    1
  • 输入#2

    7
    1 2 4 6 5 3 7

    输出#2

    0

说明/提示

In the first test case, Qingshan can only choose x=3x=3 to win, so the answer is 11 .

In the second test case, if Qingshan will choose x=4x=4 , Daniel can choose y=1y=1 . In the first turn (Qingshan's) Qingshan chooses x=3x'=3 and changes xx to 33 . In the second turn (Daniel's) Daniel chooses y=2y'=2 and changes yy to 22 . Qingshan can't choose x=2x'=2 because y=2y=2 at this time. Then Qingshan loses.

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