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

my $op = shift @ARGV;

my $minmax = '$result ? $_[0] : $_[1];';
my $settruth = '$result ? 1 : 0;';

my %ops = (
    'add'      => { 'op' => '+' },
    'multiply' => { 'op' => '*' },
    'subtract' => { 'op' => '-' },
    'divide'   => { 'op' => '/' },
    'lesser'   => { 'op' => '<' },
    'greater'  => { 'op' => '>' },
    'power'    => { 'op' => '**' },
    'xor'      => { 'op' => '&&', 'pre'  => '$_[0] = ! $_[0];' },
    'all'      => { 'op' => '&&', 'post' => $settruth },
    'none'     => { 'op' => '||', 'post' => $settruth, 'last' => '$tot = ! $tot; $tot += 0;' },
    'any'      => { 'op' => '||', 'post' => $settruth },
    'min'      => { 'op' => '<',  'post' => $minmax },
    'max'      => { 'op' => '>',  'post' => $minmax },
    'mean'     => { 'op' => '+',  'last' => '$tot /= scalar (@_ + 1);' },
    'geomean'  => { 'op' => '*',  'last' => '$tot = $tot ** ( 1 / scalar (@_ + 1) );' },
    'equal'    => { 'op' => '-',  'post' => '$result = $result ? 0 : $_[1];',
        'last' => 'local $" = "||"; $tot = 1 if 0 == $tot && 0 == eval "@_";'}
);

sub make_op {
    my $op = shift;
    my $result = 0;
    $ops{$op}{'sub'} = sub {
        ( eval $ops{$op}{'pre'} ) if defined $ops{$op}{'pre'};
        $result = ( eval $_[0] . $ops{$op}{'op'} . $_[1] ) + 0;
        $result = ( eval $ops{$op}{'post'} ) if defined $ops{$op}{'post'};
        return $result;
    };
}

sub do_op {
    my $op = shift;
    my $tot =  shift;
    make_op( $op ) unless (
        exists $ops{$op}{'sub'}
        && defined $ops{$op}{'sub'}
        && ref $ops{$op}{'sub'} eq 'CODE'
    );
    foreach ( @_ ) {
        $tot = $ops{$op}{'sub'}( $tot, $_ );
    }
    if ( exists $ops{$op}{'last'} ) {
        eval $ops{$op}{'last'};
    }
    return $tot;
}

printf "%-0.03f\n",  do_op( $op, @ARGV );