Problem:
Score : 1200 points

Problem Statement

You are given a permutation of 1,2,...,N: p_1,p_2,...,p_N. Determine if the state where p_i=i for every i can be reached by performing the following operation any number of times:

Choose three elements p_{i-1},p_{i},p_{i+1} (2\leq i\leq N-1) such that p_{i-1}>p_{i}>p_{i+1} and reverse the order of these three.

Constraints

3 \leq N \leq 3 × 10^5

p_1,p_2,...,p_N is a permutation of 1,2,...,N.

Input

Input is given from Standard Input in the following format:

N
p_1
:
p_N

Output

If the state where p_i=i for every i can be reached by performing the operation, print Yes; otherwise, print No.

Sample Input 1

5
5
2
1
4
3

Sample Output 1

Yes

The state where p_i=i for every i can be reached as follows:

Reverse the order of p_1,p_2,p_3. The sequence p becomes 1,2,5,4,3.

Reverse the order of p_3,p_4,p_5. The sequence p becomes 1,2,3,4,5.

Sample Input 2

4
3
2
4
1

Sample Output 2

No

Sample Input 3

7
3
2
1
6
5
4
7

Sample Output 3

Yes

Sample Input 4

6
5
3
4
1
2
6

Sample Output 4

No

Solution in Python (3.4.3) (judge verdict: Wrong Answer)

#!/usr/bin/env python3

def main():
    n = input()
    n = int(n)

    f = True
    t = 1
    x = -1
    for i in range(1, n + 1):
        p = input()
        p = int(p)
        if (p + i) % 2 == 1:
            f = False
        elif p == t:
            if x == -1 or x == i:
                t = i + 1
                x = -1
            else:
                t = i
        else:
            if (t + i) % 2 == 0:
                if x != -1:
                    f = False
                elif p != i + 2:
                    x = p
            else:
                if p != i:
                    f = False


    print('Yes' if f else 'No')


if __name__ == '__main__':
    main()