#use cgi.pm to get json as input
    my $q = CGI->new;
    my $json  = JSON->new->utf8;
    my $input = $json->decode( $q->param('POSTDATA') );
    #my $input = $q->param('POSTDATA');

    my $a = $input->{'a'};
    my $b = $input->{'b'};
    my $c = $a + $b;
    print $q->header("application/json");
    #print Dumper($input);
    print $json->encode({ c => $c });