CF146B.Lucky Mask

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 calls a mask of a positive integer $n$ the number that is obtained after successive writing of all lucky digits of number $n$ from the left to the right. For example, the mask of number $72174994$ is number $7744$ , the mask of $7$ is $7$ , the mask of $9999047$ is $47$ . Obviously, mask of any number is always a lucky number.

Petya has two numbers — an arbitrary integer $a$ and a lucky number $b$ . Help him find the minimum number $c$ (c>a) such that the mask of number $c$ equals $b$ .

The only line contains two integers $a$ and $b$ $(1<=a,b<=10^{5})$ . It is guaranteed that number $b$ is lucky.

In the only line print a single number — the number $c$ that is sought by Petya.