Vaqt limiti: 1 sekund
Xotira limiti: 64 MB
After the
lessons n groups
of schoolchildren went outside and decided to visit Polycarpus
to celebrate his birthday. We know that the i-th group consists of s_{i} friends (1 ≤ s_{i} ≤ 4), and
they want to go to Polycarpus together. They decided
to get there by taxi. Each car can carry at most four passengers. What minimum
number of cars will the children need if all members of each group should ride
in the same taxi (but one taxi can take more than one group)?
Input
The first line contains
integer n (1 ≤ n ≤ 10^{5})
— the number of groups of schoolchildren. The second line contains a sequence
of integers s_{1}, s_{2}, ..., s_{n} (1 ≤ s_{i} ≤ 4). The
integers are separated by a space, s_{i} 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 |
4 |
2 |
8 |
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.
Text from: codeforces.ru