#!/usr/bin/perl -w

use strict;
while(<>)
{
    chomp;
    print recursum($_), "\n";
}

sub recursum
{
    #
    # Copy first parameter to $_ but make a local copy, so that
    # changes made here can't hurt contents of $_ outside this
    # subroutine call.
    #
    local($_) = @_;

    #
    # Base case - if string contains just a number, we're done.
    #
    if (/^\s*(\d+)\s*$/)
    {
        return $1;
    }

    #
    # Take two numbers and the operator off the front, and put
    # everything after that into $rest.
    #
    elsif (/^\s*(\d+)\s*([+-])\s*(\d+)\s*(.*)/)
    {
        my($n1, $op, $n2, $rest) = ($1, $2, $3, $4);
        my $sum;

        #
        # Because of the regular expression, $op is either + or -, so
        # no need for elsif here.
        #
        if ($op eq '+')
        {
            $sum = $n1 + $n2;
        }
        else
        {
            $sum = $n1 - $n2;
        }

        #
        # Combine our calculation with $rest and recurse...
        #
        return recursum("$sum $rest");
    }

    else
    {
        die "Unable to parse \"$_\"\n";
    }
}