#!/usr/local/bin/perl

$totpixels=0;
$sumvals=0;
$lose = <>;
$lose = <>;
while (<>) {
  chop;
  ($value, $count, $rest) = split;
  $totpixels += $count;
  $sumvals += $count*$value;
  }
$sumvals += $totpixels/2;
printf "%d\n", $sumvals / ($totpixels / 10 + 1);

