Minimum Book Exchange Rounds

In a book exchange competition, there are n participants, each initially bringing one unique book. The goal is to determine the minimum number of exchange rounds required so that one designated participant (participant 1) exchanges her/his book with every other participant. In one round, participant 1 exchanges with one other participant. Thus, the minimum number of rounds is \(n - 1\).

Your task is to output the number of rounds followed by the list of exchange pairs. Each exchange pair should be denoted as two integers \(u\) and \(v\) where \(u = 1\) and \(v\) is the other participant.

Example:

Input:
4
1 2 3 4
Output:
3
1 2
1 3
1 4

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inputFormat

The input is given from stdin in the following format:

• The first line contains an integer \(n\) representing the number of participants.
• The second line contains \(n\) space-separated integers representing the books each participant brings.

outputFormat

Output to stdout:

• The first line contains a single integer \(n - 1\), the minimum number of exchange rounds.
• Each of the next \(n - 1\) lines should contain two integers \(1\) and \(v\) (with \(v\) ranging from 2 to \(n\)), representing an exchange between participant 1 and participant \(v\).

## sample

4
1 2 3 4

3
1 2
1 3
1 4

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