B. Derangement
time limit per test
2 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output

A permutation of n numbers is a sequence of integers from 1 to n where each number is occurred exactly once. If a permutation p1, p2, ..., pn has an index i such that pi = i, this index is called a fixed point.

A derangement is a permutation without any fixed points.

Let's denote the operation swap(a, b) as swapping elements on positions a and b.

For the given permutation find the minimal number of swap operations needed to turn it into derangement.

Input

The first line contains an integer n (2 ≤ n ≤ 200000) — the number of elements in a permutation.

The second line contains the elements of the permutation — n distinct integers from 1 to n.

Output

In the first line output a single integer k — the minimal number of swap operations needed to transform the permutation into derangement.

In each of the next k lines output two integers ai and bi (1 ≤ ai, bi ≤ n) — the arguments of swap operations.

If there are multiple possible solutions, output any of them.

Examples
Input
6
6 2 4 3 5 1
Output
1
2 5