Min Operations to Ship Products

One shipment can send two items from different locations, or a single item on its own. Find the minimum number of shipments needed to send all items.

输入格式

The first line contains n (1..100000), and the second line contains n locations (1..10⁹).

输出格式

Output a single integer answer.

样例 1

输入：

5
1 8 6 7 7

输出：

3

样例 2

输入：

3
1 1 1

输出：

3

样例 3

输入：

2
1 2

输出：

1

样例说明

Example 1: the two 7s are paired with 1 and 8 respectively, and 6 is shipped alone, for 3 in total. Example 2: items from the same location cannot ship together, so 3 shipments are needed. Example 3: the two locations ship together, 1 shipment.