PROGRAMMING:Xiao Ming's calculation problems
Xiao Ming loves mathematics very much, because mathematics is so interesting that he does math problems every day, but the clever Xiao Ming will also encounter difficulties. One day, Mr. Shan asked a question: there are n numbers in a set. How many numbers in the set are exactly equal to the sum of the other two numbers in the set? Xiao Ming can't think of a method, but he can only calculate one by one, but it's too troublesome. He knows you have worked out this problem, so he sent a request for help to you, and used the code to help Xiao Ming solve this problem.
###Input format:
Enter a number n, (0 = < n < = 100) represents the number of numbers in the set, and the next line contains the number of numbers in the set. The number size in the set does not exceed 10000
###Output format:
Output the answer to the question.
###Input example:
```in
four
1 2 3 4
```
###Output example:
The corresponding output is given here. For example:
```out
two
```
answer：If there is no answer, please comment
###Input format:
Enter a number n, (0 = < n < = 100) represents the number of numbers in the set, and the next line contains the number of numbers in the set. The number size in the set does not exceed 10000
###Output format:
Output the answer to the question.
###Input example:
```in
four
1 2 3 4
```
###Output example:
The corresponding output is given here. For example:
```out
two
```
answer：If there is no answer, please comment