PHP Syntax error, unexpected 'if' (T_IF) in your code

Can someone point out where this is going wrong? The error code is:

PHP Syntax Check: Parse error: syntax error, unexpected 'if' (T_IF) in your code on line 4

if ($sone != "") {

Code:

<?php
        if ($rvariable != "") {
            $rtotal = round((
            if ($sone != "") {
                $sone
            }
            else {
                0
            } + $stwo + $sthree + $sfour) / $rvariable, 0);
        }
?>