#!/usr/bin/perl -w
use strict;

my %sum;
while (<DATA>) {
    my ($name, $value) = split;
    $sum{$name} += $value;
}

for my $key (sort keys %sum) {
    print "$key: $sum{$key}\n";
}

__DATA__
a 1
b 5
a 3
b 7
c 9
a 2