<?php 

class Calculator{
	public static function act($left, $operator, $right){
		if($operator === "+"){
			$left = (string)$left;
			$right = (string)$right;
			
			$left = Str::rsplit($left);
			$right = Str::rsplit($right);
			
			$leftCount = count($left);
			$rightCount = count($right);
			
			if($leftCount < $rightCount)
				$count = $rightCount;
			else
				$count = $leftCount;
			
			$rs = array();
			$cb = 0;
			for($i = 0; $i < $count; $i++){
				$rs[$i] = $cb;
				$rs[$i] += isset($left[$i]) ? $left[$i] : 0;
				$rs[$i] += isset($right[$i]) ? $right[$i] : 0;
				if(strlen((string)$rs[$i]) > 9){
					$arr = Str::split($rs[$i]);
					$rs[$i] = $arr[1];
					$cb = $arr[0];
				}
				else 
					$cb = 0;
			}
			krsort($rs);
			$rs = implode("", $rs);
			$rs = preg_replace("/^0*?([^0]*)$/", "$1", $rs);
			
			return $rs ? $rs : null;
		}
		
		return null;
	}
}