a
2
b
6
a
4
f
2
b
1
a
7

%hash = {
    a => 2,
    b => 6,
    a => 4,
    f => 2,
    b => 1,
    a => 7,
};

a-->7
b-->6
f-->2

unless (exists $hash{$key} and $hash{$key} >= $value)
{
   $hash{$key} = $value;
}

#Add an element to the array of values for this key.
push @{ $hash{$key} }, $value;

use List::Util qw/max/;

print max @{ $hash{$key} };

%info;

# A loop reading two lines.
while( my $key = <> ) {
    my $value = <>;

    # Handle the case where there are an odd number of lines.
    die "Odd number of lines" unless (defined $value);

    # Assuming only non-negative values, we just silently want to compare
    # keys not seen before as having value 0. See 'perllexwarn' manual page
    no warnings 'uninitialized';

    $info{$key} = $value if $info{$key} <= $value;
}

# Dump the result
say "$_ --> $info{$_} for keys %info;