#!/usr/bin/perl
use strict;
use warnings;

my $num       = $ARGV[0] || 47;
my $length    = length $num;
my $base      = 10 ** ($length - 1);
my $base_ave  = 2  ** ($length - 1);
my $next      = 10 ** $length;
my $next_ave  = 2  ** $length;
my $ave_diff  = $next_ave - $base_ave;
my $tot_diff  = $next     - $base;
my $distance  = $num - $base;
my $guess     = $base_ave + ($distance * $ave_diff) / $tot_diff;
print "$guess\n";