A8452 | Lucky Ticket

Petya loves lucky numbers very much. Everybody knows that lucky numbers are positive integers whose decimal record contains only the lucky digits 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not.

Petya loves tickets very much. As we know, each ticket has a number that is a positive integer. Its length equals $n$ ( $n$ is always even). Petya calls a ticket lucky if the ticket's number is a lucky number and the sum of digits in the first half (the sum of the first $n/2$ digits) equals the sum of digits in the second half (the sum of the last $n/2$ digits). Check if the given ticket is lucky.

The first line contains an even integer $n$ $(2<=n<=50)$ — the length of the ticket number that needs to be checked. The second line contains an integer whose length equals exactly $n$ — the ticket number. The number may contain leading zeros.

On the first line print "YES" if the given ticket number is lucky. Otherwise, print "NO" (without the quotes).