CF288E Polo the Penguin and Lucky Numbers

Everybody knows that lucky numbers are positive integers that contain only lucky digits 4 and 7 in their decimal representation. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not. Polo the Penguin have two positive integers $ l $ and $ r $ $ (l<r) $ , both of them are lucky numbers. Moreover, their lengths (that is, the number of digits in the decimal representation without the leading zeroes) are equal to each other. Let's assume that $ n $ is the number of distinct lucky numbers, each of them cannot be greater than $ r $ or less than $ l $ , and $ a_{i} $ is the $ i $ -th (in increasing order) number of them. Find $ a_{1}·a_{2}+a_{2}·a_{3}+...+a_{n-1}·a_{n} $ . As the answer can be rather large, print the remainder after dividing it by $ 1000000007 $ ( $ 10^{9}+7 $ ).

The first line contains a positive integer $ l $ , and the second line contains a positive integer $ r $ ( $ 1

In the single line print a single integer — the answer to the problem modulo $ 1000000007 $ ( $ 10^{9}+7 $ ).