CF121D Lucky Segments

Petya loves lucky numbers. Everybody knows that lucky numbers are positive integers whose decimal representation contains only the lucky digits 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not. Petya has $ n $ number segments $ [l_{1}; r_{1}] $ , $ [l_{2}; r_{2}] $ , ..., $ [l_{n}; r_{n}] $ . During one move Petya can take any segment (let it be segment number $ i $ ) and replace it with segment $ [l_{i}+1; r_{i}+1] $ or $ [l_{i}-1; r_{i}-1] $ . In other words, during one move Petya can shift any segment to the left or to the right by a unit distance. Petya calls a number full if it belongs to each segment. That is, number $ x $ is full if for any $ i $ $ (1

The first line contains two integers $ n $ and $ k $ ( $ 1

Print on the single line the single number — the answer to the problem.

In the first sample Petya shifts the second segment by two units to the left (it turns into $ [4; 7] $ ), after that number $ 4 $ becomes full. In the second sample Petya shifts the first segment by two units to the right (it turns into $ [42; 47] $ ), and shifts the second segment by three units to the left (it turns into $ [44; 71] $ ), after that numbers $ 44 $ and $ 47 $ become full.