#!/usr/bin/perl

use strict;
use warnings;

my $n = <>;
my $total = 0;

for(my $i = 0; $i < $n; $i++) {
	my ($c, $d) = split / /, <>;
	my $num = int((($c +1) / 2)) * $d;
	$total += $num;
}

$total = $total % (10**9 + 7);
print "$total\n";

exit;