Maximum Fruit Pairs

You are given ( n ) trees, where each tree ( i ) has ( a_i ) fruits. Your task is to determine the maximum number of fruit pairs that can be collected from all trees. A fruit pair consists of two fruits. Thus, the maximum number of pairs is given by the formula:

[ \left\lfloor \frac{\sum_{i=1}^{n} a_i}{2} \right\rfloor ]

Note that you must use all the available fruits optimally to form the pairs.

inputFormat

The input consists of two lines:

• The first line contains a single integer ( n ), the number of trees.
• The second line contains ( n ) space-separated integers ( a_1, a_2, \dots, a_n ), where ( a_i ) represents the number of fruits on the ( i)-th tree.

outputFormat

Output a single integer representing the maximum number of fruit pairs that can be collected.## sample

4
1 2 3 4

5