Problem Statement

You are given $a permutation A=(A_1,\ldots,A_N)$ of $(1,2,\ldots,N)$.
Transform $A into (1,2,\ldots,N)$ by performing the following operation between 0 and N-1 times, inclusive:

• Operation: Choose any pair of integers (i,j) such that $1\leq i < j \leq N.$ Swap the elements at the i-th and j-th positions of A.

It can be proved that under the given constraints, it is always possible to transform $A into (1,2,\ldots,N)$.

Input

The input is given from Standard Input in the following format:
N
$A_1 \ldots A_N$

Output

Let K be the number of operations. Print K+1 lines.
The first line should contain K.
The $(l+1)-th line (1\leq l \leq K)$ should contain the integers i and j chosen for the l-th operation, separated by a space.
Any output that satisfies the conditions in the problem statement will be considered correct.

Constraints

• $2 \leq N \leq 2\times 10^5$
• $(A_1,\ldots,A_N)$ is a permutation of $(1,2,\ldots,N)$.
• All input values are integers.

Sample Input 1

5
3 4 1 2 5

Sample Output 1

2
1 3
2 4

The operations change the sequence as follows:

• Initially, A=(3,4,1,2,5).
• The first operation swaps the first and third elements, making A=(1,4,3,2,5).
• The second operation swaps the second and fourth elements, making A=(1,2,3,4,5).

Other outputs such as the following are also considered correct:
4
2 3
3 4
1 2
2 3

Sample Input 2

4
1 2 3 4

Sample Output 2

0

Sample Input 3

3
3 1 2

Sample Output 3

2
1 2
2 3

见题面 Input 部分

见题面 Output 部分