Sevens, Twos and Zeros

Time limit1sMemory limit128 MB

Summary

Find the smallest multiple of n that is at least n, uses only digits 7, 2, 0, and has at most 20 digits, or report NAV.

Problem

Given a natural number $n$ , write a program that outputs the smallest number $s$ satisfying all of the following conditions.

$s \ge n$ ;
written in decimal, $s$ consists only of the digits 7, 2 and 0, and does not start with 0;
the decimal representation of $s$ has at most 20 digits;
$s$ divided by $n$ leaves a remainder of 0.

A single natural number $n$ ( $0 < n < 500000$ ) is given on one line.

Output the number $s$ described above. If no such $s$ exists for the given $n$ , output the single word NAV.