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$res .= sprintf "%dw", $weeks if $we
+eks;
$res .= sprintf "%dd", $days if $days or $we
+eks;
$res .= sprintf "%dh", $hours if $hours or $days or $we
+eks;
$res .= sprintf "%dm", $minutes if $minutes or $hours or $days or $we
+eks;
$res .= sprintf '%ds', $seconds;