A8195 | Lucky Interval

Petya loves lucky numbers. We all know that lucky numbers are the positive integers whose decimal representations contain only the lucky digits 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not.

One day Petya came across an interval of numbers $[a,a+l-1]$ . Let $F(x)$ be the number of lucky digits of number $x$ . Find the minimum $b$ $(a<b)$ such, that $F(a)$ = $F(b)$ , $F(a+1)$ = $F(b+1)$ , ..., $F(a+l-1)$ = $F(b+l-1)$ .

The single line contains two integers $a$ and $l$ ( $1<=a,l<=10^{9}$ ) — the interval's first number and the interval's length correspondingly.

On the single line print number $b$ — the answer to the problem.