시간 제한메모리 제한제출정답맞힌 사람정답 비율
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## 문제

There are n towns with their own airports in the country X. We know the maximal capacities of the airports — the airport in the town Mi can have at most di connections with other towns. The task is to design the net of air connections among the towns in such a way that the town Mi has exactly di connections with other towns. We assume that connections are two-way and that each pair of towns has at most one connection between them.

Write a program that:

• reads the number of towns n and the numbers di from the standard input,
• designs the net of air connections in such a way that for every i, 1 ≤ i ≤ n, the town Mi has exactly di connections with other towns,
• writes the list of all connections to the standard output.

We assume that for the given data a solution exists. If there exists more than one solution the program should find only one. It can happen that there is no connection (even indirect) between a pair of cities.

## 입력

In the first line of the standard input there is written one integer n, 3 ≤ n ≤ 500, which is the number of towns. In the following n lines there are written positive integers di (one integer in each line).

## 출력

Your program should write all the connections of the created net to the standard output. The description of each connection consists of two positive integers separated by a single space. These integers are the numbers of two connected towns. Each description should be placed in a separate line. The numbers of towns in a line can be written in an arbitrary order. Similarly, the order of connections is not important.

## 예제 입력 1

6
2
3
2
4
1
2


## 예제 출력 1

4 2
4 1
4 3
4 6
2 5
2 1
3 6