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766. Taxi
Vaqt limiti: 1 sekund
Xotira limiti: 64 MB

### Input

The first line contains integer n (1 ≤ n ≤ 105) — the number of groups of schoolchildren. The second line contains a sequence of integers s1, s2, ...,sn (1 ≤ si ≤ 4). The integers are separated by a space, si is the number of children in the i-th group.

### Output

Print the single number — the minimum number of taxis necessary to drive all children to Polycarpus.

Samples

 № Input Output 1 5 1 2 4 3 3 4 2 8 2 3 4 4 2 1 3 1 5

Note

In the first test we can sort the children into four cars like this:

·         the third group (consisting of four children),

·         the fourth group (consisting of three children),

·         the fifth group (consisting of three children),

·         the first and the second group (consisting of one and two children, correspondingly).

There are other ways to sort the groups into four cars.